Solid-state laser for lidar system

ABSTRACT

A lidar system can include a solid-state laser to emit pulses of light. The solid-state laser can include a Q-switched laser having a gain medium and a Q-switch. The lidar system can also include a scanner configured to scan the emitted pulses of light across a field of regard and a receiver configured to detect at least a portion of the scanned pulses of light scattered by a target located a distance from the lidar system. The lidar system can also include a processor configured to determine the distance from the lidar system to the target based at least in part on a round-trip time of flight for an emitted pulse of light to travel from the lidar system to the target and back to the lidar system.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/461,394, filed Mar. 16, 2017, and entitled “SELF-RAMAN LASER FORLIDAR SYSTEM.” This and any and all other applications for which aforeign or domestic priority claim is identified in the Application DataSheet as filed with the present application are hereby incorporated byreference under 37 CFR 1.57.

BACKGROUND Technical Field

This disclosure generally relates to lidar systems.

Description of the Related Art

Light detection and ranging (lidar) is a technology that can be used tomeasure distances to remote targets. Typically, a lidar system includesa light source and an optical receiver. The light source can be, forexample, a laser which emits light having a particular operatingwavelength. The operating wavelength of a lidar system may lie, forexample, in the infrared, visible, or ultraviolet portions of theelectromagnetic spectrum. The light source emits light toward a targetwhich then scatters the light. Some of the scattered light is receivedback at the receiver. The system determines the distance to the targetbased on one or more characteristics associated with the returned light.For example, the system may determine the distance to the target basedon the time of flight of a returned light pulse.

SUMMARY

In some embodiments, a lidar system comprises: a solid-state laserconfigured to emit pulses of light, wherein the solid-state lasercomprises a Q-switched laser comprising a gain medium and a Q-switch; ascanner configured to scan the emitted pulses of light across a field ofregard; a receiver configured to detect at least a portion of thescanned pulses of light scattered by a target located a distance fromthe lidar system; and a processor configured to determine the distancefrom the lidar system to the target based at least in part on around-trip time of flight for an emitted pulse of light to travel fromthe lidar system to the target and back to the lidar system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example light detection and ranging (lidar)system.

FIG. 2 illustrates an example scan pattern produced by a lidar system.

FIG. 3 illustrates an example lidar system with an example overlapmirror.

FIG. 4 illustrates an example light-source field of view and receiverfield of view for a lidar system.

FIG. 5 illustrates an example light-source field of view and receiverfield of view with a corresponding scan direction.

FIG. 6 illustrates an example receiver field of view that is offset froma light-source field of view.

FIG. 7 illustrates an example forward-scan direction and reverse-scandirection for a light-source field of view and a receiver field of view.

FIG. 8 illustrates an example lidar system 100 that uses multiple outputbeams to scan a field of regard (FOR).

FIG. 9 illustrates an example detector array.

FIG. 10 illustrates an example passively Q-switched (PQSW) laser thatincludes a gain medium and a saturable absorber.

FIG. 11 illustrates an example passively Q-switched laser that includesan end cap.

FIG. 12 illustrates an example passively Q-switched laser that includesan air gap between the gain medium and the saturable absorber.

FIG. 13 illustrates an example optical parametric oscillator (OPO)configured to operate in an idler-resonant mode.

FIG. 14 illustrates an example optical parametric oscillator configuredto operate in a signal-resonant mode.

FIG. 15 illustrates an example optical parametric oscillator configuredto operate in a cross-resonant mode.

FIG. 16 illustrates an example idler-resonant optical parametricoscillator with an external mirror.

FIG. 17 illustrates an example signal-resonant optical parametricoscillator with an external mirror.

FIG. 18 illustrates an example self-Raman laser that includes a gainmedium and a saturable absorber.

FIG. 19 illustrates an example self-Raman laser that includes alaser-cavity mirror and an end cap.

FIG. 20 illustrates an example computer system.

DETAILED DESCRIPTION

FIG. 1 illustrates an example light detection and ranging (lidar) system100. In particular embodiments, a lidar system 100 may be referred to asa laser ranging system, a laser radar system, a LIDAR system, or a laserdetection and ranging (LADAR or ladar) system. In particularembodiments, a lidar system 100 may include a light source 110, mirror115, scanner 120, receiver 140, or controller 150. The light source 110may be, for example, a laser which emits light having a particularoperating wavelength in the infrared, visible, or ultraviolet portionsof the electromagnetic spectrum. As an example, light source 110 mayinclude a laser with an operating wavelength between approximately 1.2μm and 1.7 μm. The light source 110 emits an output beam of light 125which may be continuous-wave, pulsed, or modulated in any suitablemanner for a given application. The output beam of light 125 is directeddown range toward a remote target 130. As an example, the remote target130 may be located a distance D of approximately 1 m to 1 km from thelidar system 100.

Once the output beam 125 reaches the down range target 130, the targetmay scatter or reflect at least a portion of light from the output beam125, and some of the scattered or reflected light may return toward thelidar system 100. In the example of FIG. 1, the scattered or reflectedlight is represented by input beam 135, which passes through scanner 120and is directed by mirror 115 to receiver 140. In particularembodiments, a relatively small fraction of the light from output beam125 may return to the lidar system 100 as input beam 135. As an example,the ratio of input beam 135 average power, peak power, or pulse energyto output beam 125 average power, peak power, or pulse energy may beapproximately 10⁻¹, 10⁻², 10⁻³, 10⁻⁴, 10⁻⁵, 10⁻⁶, 10⁻⁷, 10⁻⁸, 10⁻⁹,10⁻¹⁰, 10⁻¹¹, or 10⁻¹². As another example, if a pulse of output beam125 has a pulse energy of 1 microjoule (μJ), then the pulse energy of acorresponding pulse of input beam 135 may have a pulse energy ofapproximately 100 nanojoules (nJ), 10 nJ, 1 nJ, 100 picojoules (pJ), 10pJ, 1 pJ, 100 femtojoules (fJ), 10 fJ, 1 fJ, 100 attojoules (aJ), 10 aJ,or 1 aJ. In particular embodiments, output beam 125 may be referred toas a laser beam, light beam, optical beam, emitted beam, or beam. Inparticular embodiments, input beam 135 may be referred to as a returnbeam, received beam, return light, received light, input light,scattered light, or reflected light. As used herein, scattered light mayrefer to light that is scattered or reflected by a target 130. As anexample, an input beam 135 may include: light from the output beam 125that is scattered by target 130; light from the output beam 125 that isreflected by target 130; or a combination of scattered and reflectedlight from target 130.

In particular embodiments, receiver 140 may receive or detect photonsfrom input beam 135 and generate one or more representative signals. Forexample, the receiver 140 may generate an output electrical signal 145that is representative of the input beam 135. This electrical signal 145may be sent to controller 150. In particular embodiments, controller 150may include a processor, computing system (e.g., an ASIC or FPGA), orother suitable circuitry configured to analyze one or morecharacteristics of the electrical signal 145 from the receiver 140 todetermine one or more characteristics of the target 130, such as itsdistance down range from the lidar system 100. This can be done, forexample, by analyzing the time of flight or phase modulation for a beamof light 125 transmitted by the light source 110. If lidar system 100measures a time of flight of T (e.g., T represents a round-trip time offlight for an emitted pulse of light to travel from the lidar system 100to the target 130 and back to the lidar system 100), then the distance Dfrom the target 130 to the lidar system 100 may be expressed as D=c·T/2,where c is the speed of light (approximately 3.0×10⁸ m/s). As anexample, if a time of flight is measured to be T=300 ns, then thedistance from the target 130 to the lidar system 100 may be determinedto be approximately D=45.0 m. As another example, if a time of flight ismeasured to be T=1.33 μs, then the distance from the target 130 to thelidar system 100 may be determined to be approximately D=199.5 m. Inparticular embodiments, a distance D from lidar system 100 to a target130 may be referred to as a distance, depth, or range of target 130. Asused herein, the speed of light c refers to the speed of light in anysuitable medium, such as for example in air, water, or vacuum. As anexample, the speed of light in vacuum is approximately 2.9979×10⁸ m/s,and the speed of light in air (which has a refractive index ofapproximately 1.0003) is approximately 2.9970×10⁸ m/s.

In particular embodiments, light source 110 may include a pulsed laser.As an example, light source 110 may be a pulsed laser configured toproduce or emit pulses of light with a pulse duration or pulse width ofapproximately 10 picoseconds (ps) to 20 nanoseconds (ns). As anotherexample, light source 110 may be a pulsed laser that produces pulseswith a pulse duration of approximately 200-400 ps. As another example,light source 110 may be a pulsed laser that produces pulses at a pulserepetition frequency of approximately 100 kHz to 5 MHz or a pulse period(e.g., a time between consecutive pulses) of approximately 200 ns to 10μs. In particular embodiments, light source 110 may have a substantiallyconstant pulse repetition frequency, or light source 110 may have avariable or adjustable pulse repetition frequency. As an example, lightsource 110 may be a pulsed laser that produces pulses at a substantiallyconstant pulse repetition frequency of approximately 640 kHz (e.g.,640,000 pulses per second), corresponding to a pulse period ofapproximately 1.56 μs. As another example, light source 110 may have apulse repetition frequency that can be varied from approximately 700 kHzto 3 MHz. As used herein, a pulse of light may be referred to as anoptical pulse, a light pulse, or a pulse.

In particular embodiments, light source 110 may produce a free-spaceoutput beam 125 having any suitable average optical power, and theoutput beam 125 may have optical pulses with any suitable pulse energyor peak optical power. As an example, output beam 125 may have anaverage power of approximately 1 mW, 10 mW, 100 mW, 1 W, 10 W, or anyother suitable average power. As another example, output beam 125 mayinclude pulses with a pulse energy of approximately 0.1 μJ, 1 μJ, 10 μJ,100 μJ, 1 mJ, or any other suitable pulse energy. As another example,output beam 125 may include pulses with a peak power of approximately 10W, 100 W, 1 kW, 5 kW, 10 kW, or any other suitable peak power. Anoptical pulse with a duration of 400 ps and a pulse energy of 1 μJ has apeak power of approximately 2.5 kW. If the pulse repetition frequency is500 kHz, then the average power of an output beam 125 with 1-μJ pulsesis approximately 0.5 W.

In particular embodiments, light source 110 may include a laser diode,such as for example, a Fabry-Perot laser diode, a quantum well laser, adistributed Bragg reflector (DBR) laser, a distributed feedback (DFB)laser, or a vertical-cavity surface-emitting laser (VCSEL). As anexample, light source 110 may include an aluminum-gallium-arsenide(AlGaAs) laser diode, an indium-gallium-arsenide (InGaAs) laser diode,or an indium-gallium-arsenide-phosphide (InGaAsP) laser diode. Inparticular embodiments, light source 110 may include a pulsed laserdiode with a peak emission wavelength of approximately 1400-1600 nm. Asan example, light source 110 may include a laser diode that is currentmodulated to produce optical pulses. In particular embodiments, lightsource 110 may include a pulsed laser diode followed by one or moreoptical-amplification stages. As an example, light source 110 may be afiber-laser module that includes a current-modulated laser diode with apeak wavelength of approximately 1550 nm followed by a single-stage or amulti-stage erbium-doped fiber amplifier (EDFA). As another example,light source 110 may include a continuous-wave (CW) or quasi-CW laserdiode followed by an external optical modulator (e.g., an electro-opticmodulator), and the output of the modulator may be fed into an opticalamplifier.

In particular embodiments, an output beam of light 125 emitted by lightsource 110 may be a collimated optical beam with any suitable beamdivergence, such as for example, a divergence of approximately 0.1 to3.0 milliradian (mrad). A divergence of output beam 125 may refer to anangular measure of an increase in beam size (e.g., a beam radius or beamdiameter) as output beam 125 travels away from light source 110 or lidarsystem 100. In particular embodiments, output beam 125 may have asubstantially circular cross section with a beam divergencecharacterized by a single divergence value. As an example, an outputbeam 125 with a circular cross section and a divergence of 1 mrad mayhave a beam diameter or spot size of approximately 10 cm at a distanceof 100 m from lidar system 100. In particular embodiments, output beam125 may be an astigmatic beam or may have a substantially ellipticalcross section and may be characterized by two divergence values. As anexample, output beam 125 may have a fast axis and a slow axis, where thefast-axis divergence is greater than the slow-axis divergence. Asanother example, output beam 125 may be an astigmatic beam with afast-axis divergence of 2 mrad and a slow-axis divergence of 0.5 mrad.

In particular embodiments, an output beam of light 125 emitted by lightsource 110 may be unpolarized or randomly polarized, may have nospecific or fixed polarization (e.g., the polarization may vary withtime), or may have a particular polarization (e.g., output beam 125 maybe linearly polarized, elliptically polarized, or circularly polarized).As an example, light source 110 may produce linearly polarized light,and lidar system 100 may include a quarter-wave plate that converts thislinearly polarized light into circularly polarized light. The circularlypolarized light may be transmitted as output beam 125, and lidar system100 may receive input beam 135, which may be substantially or at leastpartially circularly polarized in the same manner as the output beam 125(e.g., if output beam 125 is right-hand circularly polarized, then inputbeam 135 may also be right-hand circularly polarized). The input beam135 may pass through the same quarter-wave plate (or a differentquarter-wave plate) resulting in the input beam 135 being converted tolinearly polarized light which is orthogonally polarized (e.g.,polarized at a right angle) with respect to the linearly polarized lightproduced by light source 110. As another example, lidar system 100 mayemploy polarization-diversity detection where two polarizationcomponents are detected separately. The output beam 125 may be linearlypolarized, and the lidar system 100 may split the input beam 135 intotwo polarization components (e.g., s-polarization and p-polarization)which are detected separately by two photodiodes (e.g., a balancedphotoreceiver that includes two photodiodes).

In particular embodiments, lidar system 100 may include one or moreoptical components configured to condition, shape, filter, modify,steer, or direct the output beam 125 or the input beam 135. As anexample, lidar system 100 may include one or more lenses, mirrors,filters (e.g., bandpass or interference filters), beam splitters,polarizers, polarizing beam splitters, wave plates (e.g., half-wave orquarter-wave plates), diffractive elements, or holographic elements. Inparticular embodiments, lidar system 100 may include a telescope, one ormore lenses, or one or more mirrors to expand, focus, or collimate theoutput beam 125 to a desired beam diameter or divergence. As an example,the lidar system 100 may include one or more lenses to focus the inputbeam 135 onto an active region of receiver 140. As another example, thelidar system 100 may include one or more flat mirrors or curved mirrors(e.g., concave, convex, or parabolic mirrors) to steer or focus theoutput beam 125 or the input beam 135. For example, the lidar system 100may include an off-axis parabolic mirror to focus the input beam 135onto an active region of receiver 140. As illustrated in FIG. 1, thelidar system 100 may include mirror 115 (which may be a metallic ordielectric mirror), and mirror 115 may be configured so that light beam125 passes through the mirror 115. As an example, mirror 115 (which maybe referred to as an overlap mirror, superposition mirror, orbeam-combiner mirror) may include a hole, slot, or aperture which outputlight beam 125 passes through. As another example, mirror 115 may beconfigured so that at least 80% of output beam 125 passes through mirror115 and at least 80% of input beam 135 is reflected by mirror 115. Inparticular embodiments, mirror 115 may provide for output beam 125 andinput beam 135 to be substantially coaxial so that the two beams travelalong substantially the same optical path (albeit in oppositedirections).

In particular embodiments, lidar system 100 may include a scanner 120 tosteer the output beam 125 in one or more directions down range. As anexample, scanner 120 may include one or more scanning mirrors that areconfigured to rotate, tilt, pivot, or move in an angular manner aboutone or more axes. In particular embodiments, a flat scanning mirror maybe attached to a scanner actuator or mechanism which scans the mirrorover a particular angular range. As an example, scanner 120 may includea galvanometer scanner, a resonant scanner, a piezoelectric actuator, apolygonal scanner, a rotating-prism scanner, a voice coil motor, a DCmotor, a stepper motor, or a microelectromechanical systems (MEMS)device, or any other suitable actuator or mechanism. In particularembodiments, scanner 120 may be configured to scan the output beam 125over a 5-degree angular range, 20-degree angular range, 30-degreeangular range, 60-degree angular range, or any other suitable angularrange. As an example, a scanning mirror may be configured toperiodically rotate over a 15-degree range, which results in the outputbeam 125 scanning across a 30-degree range (e.g., a 0-degree rotation bya scanning mirror results in a 20-degree angular scan of output beam125). In particular embodiments, a field of regard (FOR) of a lidarsystem 100 may refer to an area or angular range over which the lidarsystem 100 may be configured to scan or capture distance information. Asan example, a lidar system 100 with an output beam 125 with a 30-degreescanning range may be referred to as having a 30-degree angular field ofregard. As another example, a lidar system 100 with a scanning mirrorthat rotates over a 30-degree range may produce an output beam 125 thatscans across a 60-degree range (e.g., a 60-degree FOR). In particularembodiments, lidar system 100 may have a FOR of approximately 10°, 20°,40°, 60°, 120°, or any other suitable FOR.

In particular embodiments, scanner 120 may be configured to scan theoutput beam 125 horizontally and vertically, and lidar system 100 mayhave a particular FOR along the horizontal direction and anotherparticular FOR along the vertical direction. As an example, lidar system100 may have a horizontal FOR of 10° to 120° and a vertical FOR of 2° to45°. In particular embodiments, scanner 120 may include a first mirrorand a second mirror, where the first mirror directs the output beam 125toward the second mirror, and the second mirror directs the output beam125 down range. As an example, the first mirror may scan the output beam125 along a first direction, and the second mirror may scan the outputbeam 125 along a second direction that is substantially orthogonal tothe first direction. As another example, the first mirror may scan theoutput beam 125 along a substantially horizontal direction, and thesecond mirror may scan the output beam 125 along a substantiallyvertical direction (or vice versa). In particular embodiments, scanner120 may be referred to as a beam scanner, optical scanner, or laserscanner.

In particular embodiments, one or more scanning mirrors may becommunicatively coupled to controller 150 which may control the scanningmirror(s) so as to guide the output beam 125 in a desired direction downrange or along a desired scan pattern. In particular embodiments, a scanpattern (which may be referred to as an optical scan pattern, opticalscan path, or scan path) may refer to a pattern or path along which theoutput beam 125 is directed. As an example, scanner 120 may include twoscanning mirrors configured to scan the output beam 125 across a 60°horizontal FOR and a 20° vertical FOR. The two scanner mirrors may becontrolled to follow a scan path that substantially covers the 60°×20°FOR. As an example, the scan path may result in a point cloud withpixels that substantially cover the 60°×20° FOR. The pixels may beapproximately evenly distributed across the 60°×20° FOR. Alternately,the pixels may have a particular nonuniform distribution (e.g., thepixels may be distributed across all or a portion of the 60°×20° FOR,and the pixels may have a higher density in one or more particularregions of the 60°×20° FOR).

In particular embodiments, a light source 110 may emit pulses of lightwhich are scanned by scanner 120 across a FOR of lidar system 100. Oneor more of the emitted pulses of light may be scattered by a target 130located down range from the lidar system 100, and a receiver 140 maydetect at least a portion of the pulses of light scattered by the target130. In particular embodiments, receiver 140 may be referred to as aphotoreceiver, optical receiver, optical sensor, detector,photodetector, or optical detector. In particular embodiments, lidarsystem 100 may include a receiver 140 that receives or detects at leasta portion of input beam 135 and produces an electrical signal thatcorresponds to input beam 135. As an example, if input beam 135 includesan optical pulse, then receiver 140 may produce an electrical current orvoltage pulse that corresponds to the optical pulse detected by receiver140. As another example, receiver 140 may include one or more avalanchephotodiodes (APDs) or one or more single-photon avalanche diodes(SPADs). As another example, receiver 140 may include one or more PNphotodiodes (e.g., a photodiode structure formed by a p-typesemiconductor and a n-type semiconductor) or one or more PIN photodiodes(e.g., a photodiode structure formed by an undoped intrinsicsemiconductor region located between p-type and n-type regions).Receiver 140 may have an active region or an avalanche-multiplicationregion that includes silicon, germanium, or InGaAs. The active region ofreceiver 140 may have any suitable size, such as for example, a diameteror width of approximately 50-500 μm. In particular embodiments, receiver140 may include circuitry that performs signal amplification, sampling,filtering, signal conditioning, analog-to-digital conversion,time-to-digital conversion, pulse detection, threshold detection,rising-edge detection, or falling-edge detection. As an example,receiver 140 may include a transimpedance amplifier that converts areceived photocurrent (e.g., a current produced by an APD in response toa received optical signal) into a voltage signal. The voltage signal maybe sent to pulse-detection circuitry that produces an analog or digitaloutput signal 145 that corresponds to one or more characteristics (e.g.,rising edge, falling edge, amplitude, or duration) of a received opticalpulse. As an example, the pulse-detection circuitry may perform atime-to-digital conversion to produce a digital output signal 145. Theelectrical output signal 145 may be sent to controller 150 forprocessing or analysis (e.g., to determine a time-of-flight valuecorresponding to a received optical pulse).

In particular embodiments, controller 150 may be electrically coupled orcommunicatively coupled to light source 110, scanner 120, or receiver140. As an example, controller 150 may receive electrical trigger pulsesor edges from light source 110, where each pulse or edge corresponds tothe emission of an optical pulse by light source 110. As anotherexample, controller 150 may provide instructions, a control signal, or atrigger signal to light source 110 indicating when light source 110should produce optical pulses. Controller 150 may send an electricaltrigger signal that includes electrical pulses, where each electricalpulse results in the emission of an optical pulse by light source 110.In particular embodiments, the frequency, period, duration, pulseenergy, peak power, average power, or wavelength of the optical pulsesproduced by light source 110 may be adjusted based on instructions, acontrol signal, or trigger pulses provided by controller 150. Inparticular embodiments, controller 150 may be coupled to light source110 and receiver 140, and controller 150 may determine a time-of-flightvalue for an optical pulse based on timing information associated withwhen the pulse was emitted by light source 110 and when a portion of thepulse (e.g., input beam 135) was detected or received by receiver 140.In particular embodiments, controller 150 may include circuitry thatperforms signal amplification, sampling, filtering, signal conditioning,analog-to-digital conversion, time-to-digital conversion, pulsedetection, threshold detection, rising-edge detection, or falling-edgedetection.

In particular embodiments, a lidar system 100 may be used to determinethe distance to one or more down range targets 130. By scanning thelidar system 100 across a field of regard, the system can be used to mapthe distance to a number of points within the field of regard. Each ofthese depth-mapped points may be referred to as a pixel. A collection ofpixels captured in succession (which may be referred to as a depth map,a point cloud, or a frame) may be rendered as an image or may beanalyzed to identify or detect objects or to determine a shape ordistance of objects within the FOR. As an example, a depth map may covera field of regard that extends 60° horizontally and 15° vertically, andthe depth map may include a frame of 100-2000 pixels in the horizontaldirection by 4-400 pixels in the vertical direction.

In particular embodiments, lidar system 100 may be configured torepeatedly capture or generate point clouds of a field of regard at anysuitable frame rate between approximately 0.1 frames per second (FPS)and approximately 1,000 FPS. As an example, lidar system 100 maygenerate point clouds at a frame rate of approximately 0.1 FPS, 0.5 FPS,1 FPS, 2 FPS, 5 FPS, 10 FPS, 20 FPS, 100 FPS, 500 FPS, or 1,000 FPS. Asanother example, lidar system 100 may be configured to produce opticalpulses at a rate of 5×10⁵ pulses/second (e.g., the system may determine500,000 pixel distances per second) and scan a frame of 1000×50 pixels(e.g., 50,000 pixels/frame), which corresponds to a point-cloud framerate of 10 frames per second (e.g., 10 point clouds per second). Inparticular embodiments, a point-cloud frame rate may be substantiallyfixed, or a point-cloud frame rate may be dynamically adjustable. As anexample, a lidar system 100 may capture one or more point clouds at aparticular frame rate (e.g., 1 Hz) and then switch to capture one ormore point clouds at a different frame rate (e.g., 10 Hz). A slowerframe rate (e.g., 1 Hz) may be used to capture one or morehigh-resolution point clouds, and a faster frame rate (e.g., 10 Hz) maybe used to rapidly capture multiple lower-resolution point clouds.

In particular embodiments, a lidar system 100 may be configured tosense, identify, or determine distances to one or more targets 130within a field of regard. As an example, a lidar system 100 maydetermine a distance to a target 130, where all or part of the target130 is contained within a field of regard of the lidar system 100. Allor part of a target 130 being contained within a FOR of the lidar system100 may refer to the FOR overlapping, encompassing, or enclosing atleast a portion of the target 130. In particular embodiments, target 130may include all or part of an object that is moving or stationaryrelative to lidar system 100. As an example, target 130 may include allor a portion of a person, vehicle, motorcycle, truck, train, bicycle,wheelchair, pedestrian, animal, road sign, traffic light, lane marking,road-surface marking, parking space, pylon, guard rail, traffic barrier,pothole, railroad crossing, obstacle in or near a road, curb, stoppedvehicle on or beside a road, utility pole, house, building, trash can,mailbox, tree, any other suitable object, or any suitable combination ofall or part of two or more objects.

In particular embodiments, one or more lidar systems 100 may beintegrated into a vehicle. As an example, multiple lidar systems 100 maybe integrated into a car to provide a complete 360-degree horizontal FORaround the car. As another example, 6-10 lidar systems 100, each systemhaving a 45-degree to 90-degree horizontal FOR, may be combined togetherto form a sensing system that provides a point cloud covering a360-degree horizontal FOR. The lidar systems 100 may be oriented so thatadjacent FORs have an amount of spatial or angular overlap to allow datafrom the multiple lidar systems 100 to be combined or stitched togetherto form a single or continuous 360-degree point cloud. As an example,the FOR of each lidar system 100 may have approximately 1-15 degrees ofoverlap with an adjacent FOR. In particular embodiments, a vehicle mayrefer to a mobile machine configured to transport people or cargo. Forexample, a vehicle may include, may take the form of, or may be referredto as a car, automobile, motor vehicle, truck, bus, van, trailer,off-road vehicle, farm vehicle, lawn mower, construction equipment, golfcart, motorhome, taxi, motorcycle, scooter, bicycle, skateboard, train,snowmobile, watercraft (e.g., a ship or boat), aircraft (e.g., afixed-wing aircraft, helicopter, or dirigible), or spacecraft. Inparticular embodiments, a vehicle may include an internal combustionengine or an electric motor that provides propulsion for the vehicle.

In particular embodiments, one or more lidar systems 100 may be includedin a vehicle as part of an advanced driver assistance system (ADAS) toassist a driver of the vehicle in the driving process. For example, alidar system 100 may be part of an ADAS that provides information orfeedback to a driver (e.g., to alert the driver to potential problems orhazards) or that automatically takes control of part of a vehicle (e.g.,a braking system or a steering system) to avoid collisions or accidents.A lidar system 100 may be part of a vehicle ADAS that provides adaptivecruise control, automated braking, automated parking, collisionavoidance, alerts the driver to hazards or other vehicles, maintains thevehicle in the correct lane, or provides a warning if an object oranother vehicle is in a blind spot.

In particular embodiments, one or more lidar systems 100 may beintegrated into a vehicle as part of an autonomous-vehicle drivingsystem. As an example, a lidar system 100 may provide information aboutthe surrounding environment to a driving system of an autonomousvehicle. An autonomous-vehicle driving system may include one or morecomputing systems that receive information from a lidar system 100 aboutthe surrounding environment, analyze the received information, andprovide control signals to the vehicle's driving systems (e.g., steeringwheel, accelerator, brake, or turn signal). As an example, a lidarsystem 100 integrated into an autonomous vehicle may provide anautonomous-vehicle driving system with a point cloud every 0.1 seconds(e.g., the point cloud has a 10 Hz update rate, representing 10 framesper second). The autonomous-vehicle driving system may analyze thereceived point clouds to sense or identify targets 130 and theirrespective locations, distances, or speeds, and the autonomous-vehicledriving system may update control signals based on this information. Asan example, if lidar system 100 detects a vehicle ahead that is slowingdown or stopping, the autonomous-vehicle driving system may sendinstructions to release the accelerator and apply the brakes.

In particular embodiments, an autonomous vehicle may be referred to asan autonomous car, driverless car, self-driving car, robotic car, orunmanned vehicle. In particular embodiments, an autonomous vehicle mayrefer to a vehicle configured to sense its environment and navigate ordrive with little or no human input. As an example, an autonomousvehicle may be configured to drive to any suitable location and controlor perform all safety-critical functions (e.g., driving, steering,braking, parking) for the entire trip, with the driver not expected tocontrol the vehicle at any time. As another example, an autonomousvehicle may allow a driver to safely turn their attention away fromdriving tasks in particular environments (e.g., on freeways), or anautonomous vehicle may provide control of a vehicle in all but a fewenvironments, requiring little or no input or attention from the driver.

In particular embodiments, an autonomous vehicle may be configured todrive with a driver present in the vehicle, or an autonomous vehicle maybe configured to operate the vehicle with no driver present. As anexample, an autonomous vehicle may include a driver's seat withassociated controls (e.g., steering wheel, accelerator pedal, and brakepedal), and the vehicle may be configured to drive with no one seated inthe driver's seat or with little or no input from a person seated in thedriver's seat. As another example, an autonomous vehicle may not includeany driver's seat or associated driver's controls, and the vehicle mayperform substantially all driving functions (e.g., driving, steering,braking, parking, and navigating) without human input. As anotherexample, an autonomous vehicle may be configured to operate without adriver (e.g., the vehicle may be configured to transport humanpassengers or cargo without a driver present in the vehicle). As anotherexample, an autonomous vehicle may be configured to operate without anyhuman passengers (e.g., the vehicle may be configured for transportationof cargo without having any human passengers onboard the vehicle).

FIG. 2 illustrates an example scan pattern 200 produced by a lidarsystem 100. In particular embodiments, a lidar system 100 may beconfigured to scan output optical beam 125 along one or more particularscan patterns 200. In particular embodiments, a scan pattern 200 mayscan across any suitable field of regard (FOR) having any suitablehorizontal FOR (FOR_(H)) and any suitable vertical FOR (FOR_(V)). Forexample, a scan pattern 200 may have a field of regard represented byangular dimensions (e.g., FOR_(H)×FOR_(V)) 40°×30°, 90°×40°, or 60°×15°.As another example, a scan pattern 200 may have a FOR_(H) greater thanor equal to 10°, 25°, 30°, 40°, 60°, 90°, or 120°. As another example, ascan pattern 200 may have a FOR_(V) greater than or equal to 2°, 5°,10°, 15°, 20°, 30°, or 45°. In the example of FIG. 2, reference line 220represents a center of the field of regard of scan pattern 200. Inparticular embodiments, reference line 220 may have any suitableorientation, such as for example, a horizontal angle of 0° (e.g.,reference line 220 may be oriented straight ahead) and a vertical angleof 0° (e.g., reference line 220 may have an inclination of 0°), orreference line 220 may have a nonzero horizontal angle or a nonzeroinclination (e.g., a vertical angle of +10° or −10°). In FIG. 2, if thescan pattern 200 has a 60°×15° field of regard, then scan pattern 200covers a ±30° horizontal range with respect to reference line 220 and a±7.5° vertical range with respect to reference line 220. Additionally,optical beam 125 in FIG. 2 has an orientation of approximately −15°horizontal and +3° vertical with respect to reference line 220. Opticalbeam 125 may be referred to as having an azimuth of −15° and an altitudeof +3° relative to reference line 220. In particular embodiments, anazimuth (which may be referred to as an azimuth angle) may represent ahorizontal angle with respect to reference line 220, and an altitude(which may be referred to as an altitude angle, elevation, or elevationangle) may represent a vertical angle with respect to reference line220.

In particular embodiments, a scan pattern 200 may include multiplepixels 210, and each pixel 210 may be associated with one or more laserpulses and one or more corresponding distance measurements. Inparticular embodiments, a cycle of scan pattern 200 may include a totalof P_(x)×P_(y) pixels 210 (e.g., a two-dimensional distribution of P_(x)by P_(y) pixels). As an example, scan pattern 200 may include adistribution with dimensions of approximately 100-2,000 pixels 210 alonga horizontal direction and approximately 4-400 pixels 210 along avertical direction. As another example, scan pattern 200 may include adistribution of 1,000 pixels 210 along the horizontal direction by 64pixels 210 along the vertical direction (e.g., the frame size is 1000×64pixels) for a total of 64,000 pixels per cycle of scan pattern 200. Inparticular embodiments, the number of pixels 210 along a horizontaldirection may be referred to as a horizontal resolution of scan pattern200, and the number of pixels 210 along a vertical direction may bereferred to as a vertical resolution. As an example, scan pattern 200may have a horizontal resolution of greater than or equal to 100 pixels210 and a vertical resolution of greater than or equal to 4 pixels 210.As another example, scan pattern 200 may have a horizontal resolution of100-2,000 pixels 210 and a vertical resolution of 4-400 pixels 210.

In particular embodiments, each pixel 210 may be associated with adistance (e.g., a distance to a portion of a target 130 from which anassociated laser pulse was scattered) or one or more angular values. Asan example, a pixel 210 may be associated with a distance value and twoangular values (e.g., an azimuth and altitude) that represent theangular location of the pixel 210 with respect to the lidar system 100.A distance to a portion of target 130 may be determined based at leastin part on a time-of-flight measurement for a corresponding pulse. Anangular value (e.g., an azimuth or altitude) may correspond to an angle(e.g., relative to reference line 220) of output beam 125 (e.g., when acorresponding pulse is emitted from lidar system 100) or an angle ofinput beam 135 (e.g., when an input signal is received by lidar system100). In particular embodiments, an angular value may be determinedbased at least in part on a position of a component of scanner 120. Asan example, an azimuth or altitude value associated with a pixel 210 maybe determined from an angular position of one or more correspondingscanning mirrors of scanner 120.

FIG. 3 illustrates an example lidar system 100 with an example overlapmirror 115. In particular embodiments, a lidar system 100 may include alight source 110 configured to emit pulses of light and a scanner 120configured to scan at least a portion of the emitted pulses of lightacross a field of regard. As an example, the light source 110 mayinclude a pulsed solid-state laser, and the optical pulses produced bythe solid-state laser may be directed through aperture 310 of overlapmirror 115 and then coupled to scanner 120. In particular embodiments, alidar system 100 may include a receiver 140 configured to detect atleast a portion of the scanned pulses of light scattered by a target 130located a distance D from the lidar system 100. As an example, one ormore pulses of light that are directed down range from lidar system 100by scanner 120 (e.g., as part of output beam 125) may scatter off atarget 130, and a portion of the scattered light may propagate back tothe lidar system 100 (e.g., as part of input beam 135) and be detectedby receiver 140.

In particular embodiments, lidar system 100 may include one or moreprocessors (e.g., controller 150) configured to determine a distance Dfrom the lidar system 100 to a target 130 based at least in part on around-trip time of flight for an emitted pulse of light to travel fromthe lidar system 100 to the target 130 and back to the lidar system 100.The target 130 may be at least partially contained within a field ofregard of the lidar system 100 and located a distance D from the lidarsystem 100 that is less than or equal to a maximum range R_(MAX) of thelidar system 100. In particular embodiments, a maximum range (which maybe referred to as a maximum distance) of a lidar system 100 may refer tothe maximum distance over which the lidar system 100 is configured tosense or identify targets 130 that appear in a field of regard of thelidar system 100. The maximum range of lidar system 100 may be anysuitable distance, such as for example, 25 m, 50 m, 100 m, 200 m, 500 m,or 1 km. As an example, a lidar system 100 with a 200-m maximum rangemay be configured to sense or identify various targets 130 located up to200 m away from the lidar system 100. For a lidar system 100 with a200-m maximum range (R_(MAX)=200 m), the time of flight corresponding tothe maximum range is approximately 2·R_(MAX)/c≈1.33 μs.

In particular embodiments, light source 110, scanner 120, and receiver140 may be packaged together within a single housing, where a housingmay refer to a box, case, or enclosure that holds or contains all orpart of a lidar system 100. As an example, a lidar-system enclosure maycontain a light source 110, overlap mirror 115, scanner 120, andreceiver 140 of a lidar system 100. Additionally, the lidar-systemenclosure may include a controller 150, or a controller 150 may belocated remotely from the enclosure. The lidar-system enclosure may alsoinclude one or more electrical connections for conveying electricalpower or electrical signals to or from the enclosure.

In particular embodiments, light source 110 may include an eye-safelaser. An eye-safe laser may refer to a laser or a light source with anemission wavelength, average power, peak power, peak intensity, pulseenergy, beam size, beam divergence, or exposure time such that emittedlight from the laser presents little or no possibility of causing damageto a person's eyes. As an example, light source 110 may be classified asa Class 1 laser product (as specified by the 60825-1 standard of theInternational Electrotechnical Commission (IEC)) or a Class I laserproduct (as specified by Title 21, Section 1040.10 of the United StatesCode of Federal Regulations (CFR)) that is safe under all conditions ofnormal use. In particular embodiments, light source 110 may include aneye-safe laser (e.g., a Class 1 or a Class I laser) configured tooperate at any suitable wavelength between approximately 1400 nm andapproximately 1700 nm. As an example, light source 110 may include aneye-safe laser with an operating wavelength between approximately 1400nm and approximately 1600 nm. As another example, light source 110 mayinclude an eye-safe laser with an operating wavelength betweenapproximately 1530 nm and approximately 1560 nm. As another example,light source 110 may include a solid-state laser, where the solid-statelaser is an eye-safe laser with an operating wavelength betweenapproximately 1400 nm and approximately 1600 nm.

In particular embodiments, scanner 120 may include one or more mirrors,where each mirror is mechanically driven by a galvanometer scanner, aresonant scanner, a MEMS device, a voice coil motor, or any suitablecombination thereof. A galvanometer scanner (which may be referred to asa galvanometer actuator) may include a galvanometer-based scanning motorwith a magnet and coil. When an electrical current is supplied to thecoil, a rotational force is applied to the magnet, which causes a mirrorattached to the galvanometer scanner to rotate. The electrical currentsupplied to the coil may be controlled to dynamically change theposition of the galvanometer mirror. A resonant scanner (which may bereferred to as a resonant actuator) may include a spring-like mechanismdriven by an actuator to produce a periodic oscillation at asubstantially fixed frequency (e.g., 1 kHz). A MEMS-based scanningdevice may include a mirror with a diameter between approximately 1 and10 mm, where the mirror is rotated using electromagnetic orelectrostatic actuation. A voice coil motor (which may be referred to asa voice coil actuator) may include a magnet and coil. When an electricalcurrent is supplied to the coil, a translational force is applied to themagnet, which causes a mirror attached to the magnet to move or rotate.

In particular embodiments, a scanner 120 may include any suitable numberof mirrors driven by any suitable number of mechanical actuators. As anexample, a scanner 120 may include a single mirror configured to scan anoutput beam 125 along a single direction (e.g., a scanner 120 may be aone-dimensional scanner that scans along a horizontal or verticaldirection). The mirror may be driven by one actuator (e.g., agalvanometer) or two actuators configured to drive the mirror in apush-pull configuration. As another example, a scanner 120 may include asingle mirror that scans an output beam 125 along two directions (e.g.,horizontal and vertical). The mirror may be driven by two actuators,where each actuator provides rotational motion along a particulardirection or about a particular axis. As another example, a scanner 120may include two mirrors, where one mirror scans an output beam 125 alonga horizontal direction and the other mirror scans the output beam 125along a vertical direction. In the example of FIG. 3, scanner 120includes two mirrors, mirror 300A and mirror 300B. Mirror 300A may scanoutput beam 125 along a substantially horizontal direction, and mirror300B may scan the output beam 125 along a substantially verticaldirection.

In particular embodiments, a scanner 120 may include two mirrors, whereeach mirror is driven by a corresponding galvanometer scanner. As anexample, scanner 120 may include a galvanometer actuator that scansmirror 300A along a first direction (e.g., horizontal), and scanner 120may include another galvanometer actuator that scans mirror 300B along asecond direction (e.g., vertical). In particular embodiments, a scanner120 may include two mirrors, where one mirror is driven by a resonantactuator and the other mirror is driven by a galvanometer actuator. Asan example, a resonant actuator may scan mirror 300A along a firstdirection, and a galvanometer actuator may scan mirror 300B along asecond direction. The first and second directions may be substantiallyorthogonal to one another. As an example, the first direction may besubstantially horizontal, and the second direction may be substantiallyvertical, or vice versa. In particular embodiments, a scanner 120 mayinclude one mirror driven by two actuators which are configured to scanthe mirror along two substantially orthogonal directions. As an example,one mirror may be driven along a substantially horizontal direction by aresonant actuator or a galvanometer actuator, and the mirror may also bedriven along a substantially vertical direction by a galvanometeractuator. As another example, a mirror may be driven along twosubstantially orthogonal directions by two resonant actuators.

In particular embodiments, a scanner 120 may include a mirror configuredto be scanned along one direction by two actuators arranged in apush-pull configuration. Driving a mirror in a push-pull configurationmay refer to a mirror that is driven in one direction by two actuators.The two actuators may be located at opposite ends or sides of themirror, and the actuators may be driven in a cooperative manner so thatwhen one actuator pushes on the mirror, the other actuator pulls on themirror, and vice versa. As an example, a mirror may be driven along ahorizontal or vertical direction by two voice coil actuators arranged ina push-pull configuration. In particular embodiments, a scanner 120 mayinclude one mirror configured to be scanned along two axes, where motionalong each axis is provided by two actuators arranged in a push-pullconfiguration. As an example, a mirror may be driven along a horizontaldirection by two resonant actuators arranged in a horizontal push-pullconfiguration, and the mirror may be driven along a vertical directionby another two resonant actuators arranged in a vertical push-pullconfiguration.

In particular embodiments, a scanner 120 may include two mirrors whichare driven synchronously so that the output beam 125 is directed alongany suitable scan pattern 200. As an example, a galvanometer actuatormay drive mirror 300A with a substantially linear back-and-forth motion(e.g., the galvanometer may be driven with a substantiallytriangle-shaped waveform) that causes output beam 125 to trace asubstantially horizontal back-and-forth pattern. Additionally, anothergalvanometer actuator may scan mirror 300B relatively slowly along asubstantially vertical direction. For example, the two galvanometers maybe synchronized so that for every 64 horizontal traces, the output beam125 makes a single trace along a vertical direction. As another example,a resonant actuator may drive mirror 300A along a substantiallyhorizontal direction, and a galvanometer actuator may scan mirror 300Brelatively slowly along a substantially vertical direction.

In particular embodiments, a scanner 120 may include one mirror drivenby two or more actuators, where the actuators are driven synchronouslyso that the output beam 125 is directed along a particular scan pattern200. As an example, one mirror may be driven synchronously along twosubstantially orthogonal directions so that the output beam 125 followsa scan pattern 200 that includes substantially straight lines. Inparticular embodiments, a scanner 120 may include two mirrors drivensynchronously so that the synchronously driven mirrors trace out a scanpattern 200 that includes substantially straight lines. As an example,the scan pattern 200 may include a series of substantially straightlines directed substantially horizontally, vertically, or along anyother suitable direction. The straight lines may be achieved by applyinga dynamically adjusted deflection along a vertical direction (e.g., witha galvanometer actuator) as an output beam 125 is scanned along asubstantially horizontal direction (e.g., with a galvanometer orresonant actuator). If a vertical deflection is not applied, the outputbeam 125 may trace out a curved path as it scans from side to side. Byapplying a vertical deflection as the mirror is scanned horizontally, ascan pattern 200 that includes substantially straight lines may beachieved. In particular embodiments, a vertical actuator may be used toapply both a dynamically adjusted vertical deflection as the output beam125 is scanned horizontally as well as a discrete vertical offsetbetween each horizontal scan (e.g., to step the output beam 125 to asubsequent row of a scan pattern 200).

In the example of FIG. 3, lidar system 100 produces an output beam 125and receives light from an input beam 135. The output beam 125, whichincludes at least a portion of the pulses of light emitted by lightsource 110, may be scanned across a field of regard. The input beam 135may include at least a portion of the scanned pulses of light which arescattered by one or more targets 130 and detected by receiver 140. Inparticular embodiments, output beam 125 and input beam 135 may besubstantially coaxial. The input and output beams being substantiallycoaxial may refer to the beams being at least partially overlapped orsharing a common propagation axis so that input beam 135 and output beam125 travel along substantially the same optical path (albeit in oppositedirections). As output beam 125 is scanned across a field of regard, theinput beam 135 may follow along with the output beam 125 so that thecoaxial relationship between the two beams is maintained.

In particular embodiments, a lidar system 100 may include an overlapmirror 115 configured to overlap the input beam 135 and output beam 125so that they are substantially coaxial. In FIG. 3, the overlap mirror115 includes a hole, slot, or aperture 310 which the output beam 125passes through and a reflecting surface 320 that reflects at least aportion of the input beam 135 toward the receiver 140. The overlapmirror 115 may be oriented so that input beam 135 and output beam 125are at least partially overlapped. In particular embodiments, input beam135 may pass through a lens 330 which focuses the beam onto an activeregion of the receiver 140. The active region may refer to an area overwhich receiver 140 may receive or detect input light. The active regionmay have any suitable size or diameter d, such as for example, adiameter of approximately 25 μm, 50 μm, 80 μm, 100 μm, 200 μm, 500 μm, 1mm, 2 mm, or 5 mm. In particular embodiments, overlap mirror 115 mayhave a reflecting surface 320 that is substantially flat or thereflecting surface 320 may be curved (e.g., mirror 115 may be anoff-axis parabolic mirror configured to focus the input beam 135 onto anactive region of the receiver 140).

In particular embodiments, aperture 310 may have any suitable size ordiameter Φ₁, and input beam 135 may have any suitable size or diameterΦ₂, where Φ₂ is greater than Φ₁. As an example, aperture 310 may have adiameter 4:13 ₁ of approximately 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 5 mm,or 10 mm, and input beam 135 may have a diameter Φ₂ of approximately 2mm, 5 mm, 10 mm, 15 mm, 20 mm, 30 mm, 40 mm, or 50 mm. In particularembodiments, reflective surface 320 of overlap mirror 115 may reflectgreater than or equal to 70% of input beam 135 toward the receiver 140.As an example, if reflective surface 320 has a reflectivity R at anoperating wavelength of the light source 110, then the fraction of inputbeam 135 directed toward the receiver 140 may be expressed asR×[1−(Φ₁/Φ₂)²]. For example, if R is 95%, Φ₁ is 2 mm, and Φ₂ is 10 mm,then approximately 91% of input beam 135 may be directed toward thereceiver 140 by reflective surface 320.

FIG. 4 illustrates an example light-source field of view (FOV_(L)) andreceiver field of view (FOV_(R)) for a lidar system 100. The lightsource 110 may emit pulses of light as the FOV_(L) and FOV_(R) arescanned across a field of regard (FOR) of the lidar system 100. Inparticular embodiments, a light-source field of view may refer to anangular cone illuminated by the light source 110 at a particular instantof time. Similarly, a receiver field of view may refer to an angularcone over which the receiver 140 may receive or detect light at aparticular instant of time, and any light outside the receiver field ofview may not be received or detected. As an example, as the light-sourcefield of view is scanned across a field of regard, a portion of a pulseof light emitted by the light source 110 may be sent down range fromlidar system 100, and the pulse of light may be sent in the directionthat the FOV_(L) is pointing at the time the pulse is emitted. The pulseof light may scatter off a target 130, and the receiver 140 may receiveand detect a portion of the scattered light that is directed along orcontained within the FOV_(R).

In particular embodiments, scanner 120 may be configured to scan both alight-source field of view and a receiver field of view across a fieldof regard of the lidar system 100. Multiple pulses of light may beemitted and detected as the scanner 120 scans the FOV_(L) and FOV_(R)across the field of regard of the lidar system 100 while tracing out ascan pattern 200. In particular embodiments, the light-source field ofview and the receiver field of view may be scanned synchronously withrespect to one another, so that as the FOV_(L) is scanned across a scanpattern 200, the FOV_(R) follows substantially the same path at the samescanning speed. Additionally, the FOV_(L) and FOV_(R) may maintain thesame relative position to one another as they are scanned across thefield of regard. As an example, the FOV_(L) may be substantiallyoverlapped with or centered inside the FOV_(R) (as illustrated in FIG.4), and this relative positioning between FOV_(L) and FOV_(R) may bemaintained throughout a scan. As another example, the FOV_(R) may lagbehind the FOV_(L) by a particular, fixed amount throughout a scan(e.g., the FOV_(R) may be offset from the FOV_(L) in a directionopposite the scan direction).

In particular embodiments, the FOV_(L) may have an angular size orextent Θ_(L) that is substantially the same as or that corresponds tothe divergence of the output beam 125, and the FOV_(R) may have anangular size or extent Θ_(R) that corresponds to an angle over which thereceiver 140 may receive and detect light. In particular embodiments,the receiver field of view may be any suitable size relative to thelight-source field of view. As an example, the receiver field of viewmay be smaller than, substantially the same size as, or larger than theangular extent of the light-source field of view. In particularembodiments, the light-source field of view may have an angular extentof less than or equal to 50 milliradians, and the receiver field of viewmay have an angular extent of less than or equal to 50 milliradians. TheFOV_(L) may have any suitable angular extent Θ_(L), such as for example,approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2 mrad, 3mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. Similarly, theFOV_(R) may have any suitable angular extent Θ_(R), such as for example,approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2 mrad, 3mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. In particularembodiments, the light-source field of view and the receiver field ofview may have approximately equal angular extents. As an example, Θ_(L)and Θ_(R) may both be approximately equal to 1 mrad, 2 mrad, or 3 mrad.In particular embodiments, the receiver field of view may be larger thanthe light-source field of view, or the light-source field of view may belarger than the receiver field of view. As an example, Θ_(L) may beapproximately equal to 1.5 mrad, and Θ_(R) may be approximately equal to3 mrad.

In particular embodiments, a pixel 210 may represent or may correspondto a light-source field of view. As the output beam 125 propagates fromthe light source 110, the diameter of the output beam 125 (as well asthe size of the corresponding pixel 210) may increase according to thebeam divergence Θ_(L). As an example, if the output beam 125 has a Θ_(L)of 2 mrad, then at a distance of 100 m from the lidar system 100, theoutput beam 125 may have a size or diameter of approximately 20 cm, anda corresponding pixel 210 may also have a corresponding size or diameterof approximately 20 cm. At a distance of 200 m from the lidar system100, the output beam 125 and the corresponding pixel 210 may each have adiameter of approximately 40 cm.

FIG. 5 illustrates an example light-source field of view and receiverfield of view with a corresponding scan direction. In particularembodiments, scanner 120 may scan the FOV_(L) and FOV_(R) along anysuitable scan direction or combination of scan directions, such as forexample, left to right, right to left, upward, downward, or any suitablecombination thereof. As an example, the FOV_(L) and FOV_(R) may follow aleft-to-right scan direction (as illustrated in FIG. 5) across a fieldof regard, and then the FOV_(L) and FOV_(R) may travel back across thefield of regard in a right-to-left scan direction. In particularembodiments, a light-source field of view and a receiver field of viewmay be at least partially overlapped during scanning. As an example, theFOV_(L) and FOV_(R) may have any suitable amount of angular overlap,such as for example, approximately 1%, 2%, 5%, 10%, 25%, 50%, 75%, 90%,or 100% of angular overlap. As another example, if Θ_(L) and Θ_(R) are 2mrad, and FOV_(L) and FOV_(R) are offset from one another by 1 mrad,then FOV_(L) and FOV_(R) may be referred to as having a 50% angularoverlap. As another example, the FOV_(L) and FOV_(R) may besubstantially coincident with one another and may have an angularoverlap of approximately 100%. In the example of FIG. 5, the FOV_(L) andFOV_(R) are approximately the same size and have an angular overlap ofapproximately 90%.

FIG. 6 illustrates an example receiver field of view that is offset froma light-source field of view. In particular embodiments, a FOV_(L) andFOV_(R) may be scanned along a particular scanning direction, and theFOV_(R) may be offset from the FOV_(L) in a direction opposite thescanning direction. In the example of FIG. 6, the FOV_(L) and FOV_(R)are approximately the same size, and the FOV_(R) lags behind the FOV_(L)so that the FOV_(L) and FOV_(R) have an angular overlap of approximately5%. In particular embodiments, the FOV_(R) may be configured to lagbehind the FOV_(L) to produce any suitable angular overlap, such as forexample, an angular overlap of less than or equal to 50%, 25%, 5%, 1%,or 0.1%. After a pulse of light is emitted by light source 110, thepulse may scatter from a target 130, and some of the scattered light maypropagate back to the lidar system 100 along a path that corresponds tothe orientation of the light-source field of view at the time the pulsewas emitted. As the pulse of light propagates to and from the target130, the receiver field of view moves in the scan direction andincreases its overlap with the previous location of the light-sourcefield of view (e.g., the location of the light-source field of view whenthe pulse was emitted). For a close-range target (e.g., a target 130located within 20% of the maximum range of the lidar system), when thereceiver 140 detects scattered light from the emitted pulse, thereceiver field of view may overlap less than or equal to 20% of theprevious location of the light-source field of view. The receiver 140may receive less than or equal to 20% of the scattered light thatpropagates back to the lidar system 100 along the path that correspondsto the orientation of the light-source field of view at the time thepulse was emitted. However, since the target 130 is located relativelyclose to the lidar system 100, the receiver 140 may still receive asufficient amount of light to produce a signal indicating that a pulsehas been detected. For a midrange target (e.g., a target 130 locatedbetween 20% and 80% of the maximum range of the lidar system 100), whenthe receiver 140 detects the scattered light, the receiver field of viewmay overlap between 20% and 80% of the previous location of thelight-source field of view. For a target 130 located a distance greaterthan or equal to 80% of the maximum range of the lidar system 100, whenthe receiver 140 detects the scattered light, the receiver field of viewmay overlap greater than or equal to 80% of the previous location of thelight-source field of view. For a target 130 located at the maximumrange from the lidar system 100, when the receiver 140 detects thescattered light, the receiver field of view may be substantiallyoverlapped with the previous location of the light-source field of view,and the receiver 140 may receive substantially all of the scatteredlight that propagates back to the lidar system 100.

FIG. 7 illustrates an example forward-scan direction and reverse-scandirection for a light-source field of view and a receiver field of view.In particular embodiments, a lidar system 100 may be configured so thatthe FOV_(R) is larger than the FOV_(L), and the receiver andlight-source FOVs may be substantially coincident, overlapped, orcentered with respect to one another. As an example, the FOV_(R) mayhave a diameter or angular extent Θ_(R), that is approximately 1.5×, 2×,3×, 4×, 5×, or 10× larger than the diameter or angular extent Θ_(L) ofthe FOV_(L). In the example of FIG. 7, the diameter of the receiverfield of view is approximately 2 times larger than the diameter of thelight-source field of view, and the two FOVs are overlapped and centeredwith respect to one another. The receiver field of view being largerthan the light-source field of view may allow the receiver 140 toreceive scattered light from emitted pulses in both scan directions(forward scan or reverse scan). In the forward-scan directionillustrated in FIG. 7, scattered light may be received primarily by theleft side of the FOV_(R), and in the reverse-scan direction, scatteredlight may be received primarily by the right side of the FOV_(R). Forexample, as a pulse of light propagates to and from a target 130 duringa forward scan, the FOV_(R) scans to the right, and scattered light thatreturns to the lidar system 100 may be received primarily by the leftportion of the FOV_(R).

In particular embodiments, a lidar system 100 may perform a series offorward and reverse scans. As an example, a forward scan may include theFOV_(L) and the FOV_(R) being scanned horizontally from left to right,and a reverse scan may include the two fields of view being scanned fromright to left. As another example, a forward scan may include theFOV_(L) and the FOV_(R) being scanned along any suitable direction(e.g., along a 45-degree angle), and a reverse scan may include the twofields of view being scanned along a substantially opposite direction.In particular embodiments, the forward and reverse scans may trace pathsthat are adjacent to or displaced with respect to one another. As anexample, a reverse scan may follow a line in the field of regard that isdisplaced above, below, to the left of, or to the right of a previousforward scan. As another example, a reverse scan may scan a row in thefield of regard that is displaced below a previous forward scan, and thenext forward scan may be displaced below the reverse scan. The forwardand reverse scans may continue in an alternating manner with each scanbeing displaced with respect to the previous scan until a complete fieldof regard has been covered. Scans may be displaced with respect to oneanother by any suitable fixed or adjustable angular amount, such as forexample, by approximately 0.05°, 0.1°, 0.2°, 0.5°, 1°, 2°, 5°, or 10°.

FIG. 8 illustrates an example lidar system 100 that uses multiple outputbeams to scan a field of regard (FOR). In particular embodiments, alidar system 100 may emit two or more angularly separated output beamswhich are used to scan a FOR. As an example, a lidar system 100 may use2, 3, 4, 5, 10, 15, 20, 50, or any other suitable number of output beams125 to simultaneously scan a FOR. In the example of FIG. 8, lidar system100 produces four angularly separated output beams (125A, 125B, 125C,and 125D) to simultaneously scan across the FOR, which is subdividedinto four corresponding regions (350A, 350B, 350C, and 350D). Each ofthe output beams (125A, 125B, 125C, and 125D) may be configured to scanacross a respective region (350A, 350B, 350C, and 350D) of the FOR. Theangularly separated output beams may be scanned synchronously so thateach output beam follows substantially the same scan pattern within theoutput beam's corresponding scan region, and the output beams maintainsubstantially the same relative position to one another as they arescanned. In FIG. 8, output beams 125A, 125B, 125C, and 125D scan acrossregions 350A, 350B, 350C, and 350D, respectively, and each output beammay follow a scan pattern having approximately the same shape.

In particular embodiments, the multiple output beams produced by a lidarsystem 100 may have a separation angle α of approximately 0.5°, 1°, 2°,5°, 10°, 20°, or any other suitable separation angle. If a FOR isdivided into N regions, then the separation angle α between adjacentbeams may be approximately FOR_(V)/N. In the example of FIG. 8, the FORis divided into N=4 regions which are scanned by the corresponding fouroutput beams 125A, 125B, 125C, and 125D. If FOR_(V) is 20°, then theseparation angle α between adjacent beams is approximately 5°. Inparticular embodiments, each optical pulse emitted by a light source 110may be split into N pulses, where N is 2, 3, 4, 5, 10, 15, 20, 50, orany other suitable value. In the example of FIG. 8, each emitted pulseis split into four pulses which are directed along the four respectiveoutput beams 125A, 125B, 125C, and 125D. In particular embodiments, anemitted pulse may be approximately evenly split into N pulses, whereeach of the N pulses has approximately 1/N of the energy of the emittedpulse. As an example, an emitted pulse with a pulse energy ofapproximately 4 μJ may be split into 4 pulses, where each of the splitpulses has an energy of approximately 1 μJ.

In particular embodiments, a lidar system 100 may include a splitterconfigured to receive pulses of light emitted by a light source 110 andsplit each received pulse of light into two or more angularly separatedpulses of light which are scanned across a FOR. In particularembodiments, a splitter may include a diffractive optical element, aholographic optical element, a polarizing beam splitter, anon-polarizing beam splitter, or a beam splitter with a metallic ordielectric coating. As an example, a splitter (which may be referred toas a multispot beam generator, an array beam generator, a beam splitter,or a pixelator) may include a diffractive element or a holographicelement that divides an input beam into two or more output beams. Adiffractive beam splitter may have a repetitive pattern etched ordeposited on one of its surfaces. The repetitive pattern may produce acorresponding periodic refractive-index or absorption variation thatdiffracts an input optical beam to produce N angularly separated outputbeams. A holographic beam splitter may include a bulk material with arepetitive variation in its refractive index or absorption. As anexample, a holographic beam splitter may have a bulk refractive-indexvariation that results in the splitting of an input optical beam into Nangularly separated output beams.

In particular embodiments, a splitter may be positioned before or aftera scanner 120. As an example, a splitter may receive emitted pulses oflight after they pass through a scanner 120. As another example, asplitter may be positioned before a scanner 120 so that the splitterreceives pulses of light emitted by the light source 110, and thescanner 120 receives the pulses of light after they are split by thesplitter. In particular embodiments, a scanner 120 may scan angularlyseparated pulses of light along a scanning direction, and the angularlyseparated pulses of light produced by a splitter may be split along adirection that is approximately orthogonal to the scanning direction. Asan example, if the scanning direction is substantially vertical, thenthe angularly separated pulses of light may be split along asubstantially horizontal direction. In the example of FIG. 8, thescanning direction is substantially horizontal, and the angularlyseparated pulses of light are split along a substantially verticaldirection. In particular embodiments, splitting a beam along a directionthat is approximately orthogonal to a scanning direction may allow alidar system 100 to simultaneously scan multiple regions of a FOR. InFIG. 8, the four output beams 125A, 125B, 125C, and 125B may be used tosimultaneously scan the four respective regions 350A, 350B, 350C, and350D.

In particular embodiments, scanning a FOR with N split pulses may resultin an increase in a lidar-system frame rate by a factor of N. As anexample, for a light source 110 that produces pulses at a pulserepetition frequency f, if each pulse is split into N pulses, then theeffective pulse repetition frequency may be increased to Nxf. As anotherexample, for a light source 110 with a pulse repetition frequency of 100kHz, a frame with 50,000 pixels 210 may be scanned with a frame rate of2 frames per second. If each emitted pulse is split into N=5 pulses,then the effective pulse repetition frequency is increased to 500 kHz,and the frame rate increases to 10 frames per second.

FIG. 9 illustrates an example detector array 360. In particularembodiments, a receiver 140 may include an array 360 of two or moredetector elements. Each detector element may include an APD, SPAD, orphotodiode and may be configured to detect scattered light from arespective pulse of angularly separated pulses of light which arescanned across a FOR. A detector array 360 may include any suitablearrangement of detector elements. As an example, a detector array 360may include a one-dimensional horizontal or vertical arrangement ofdetector elements. As another example, a detector array 360 may includea two-dimensional arrangement of detector elements (e.g., 8 detectorelements arranged in a 2×4 grid). In the example of FIG. 9, detectorarray 360 includes a one-dimensional vertical arrangement of fourdetector elements (APDs 370A, 370B, 370C, and 370D). In particularembodiments, an arrangement of detector-array elements may correspond toa direction along which the output beams of a lidar system 100 aresplit. As an example, if an output beam is split along a verticaldirection, the elements of a detector array 360 may be arranged along acorresponding direction.

In particular embodiments, a lidar system 100 may include a light source110 and a splitter configured to split a pulse of light emitted by thelight source 110 into N angularly separated pulses of light. The Nangularly separated pulses of light may be used to scan N respectiveregions of a FOR. Additionally, the lidar system 100 may include adetector array 360 with N detector elements, where each detector elementis configured to receive scattered light from a corresponding angularlyseparated pulse of light. The detector array 360 in FIG. 9 may beincluded in a receiver 140 of lidar system 100 of FIG. 8, and APDs 370A,370B, 370C, and 370D may be configured to detect scattered lightassociated with output beams 125A, 125B, 125C, and 125D, respectively.As an example, APD 370A may detect scattered light from output beam125A, which is used to scan across region 350A of the FOR. Similarly,APDs 370B, 370C, and 370D may detect scattered light from output beams125B, 125C, and 125D, respectively, which are used to scan acrossregions 350B, 350C, and 350D, respectively.

In particular embodiments, a light source 110 of a lidar system 100 mayinclude a solid-state laser. In particular embodiments, a solid-statelaser may refer to a laser that includes a solid-state, glass, orcrystal-based gain medium. As an example, the gain medium of asolid-state laser may include rare-earth ions in a crystal or glass hostmaterial that are optically pumped to provide optical gain. Inparticular embodiments, optical pumping (or, pumping) may refer toproviding energy to a gain medium, where the energy is provided by anoptical source (e.g., a pump laser diode). The gain medium may absorblight from a pump laser and may be “pumped” or promoted into excitedstates that provide optical amplification to particular wavelengths oflight through stimulated emission. As an example, the gain medium may bea glass or crystal host material doped with rare-earth ions, such as forexample, erbium (Er), neodymium (Nd), ytterbium (Yb), praseodymium (Pr),holmium (Ho), thulium (Tm), dysprosium (Dy), any other suitablerare-earth element, or any suitable combination of rare-earth elements.The rare-earth dopants (which may be referred to as gain material or asgain-material dopants) may absorb pump light and provide optical gain toparticular wavelengths of light that circulate within a solid-statelaser cavity. Herein, reference to a rare-earth element (e.g., erbium orytterbium) may correspond to an ion of that rare-earth element (e.g.,trivalent erbium (Er³⁺) or trivalent ytterbium (Yb³⁺)).

In particular embodiments, a glass host material for a gain medium mayinclude any suitable glass material, such as for example, a silicateglass (e.g., fused silica or borosilicate glass) or a phosphate glass.As an example, a gain medium of a solid-state laser may include aphosphate glass doped with erbium, ytterbium, or a combination of erbiumand ytterbium. In particular embodiments, a crystalline host materialfor a gain medium may include any suitable member of the garnet,perovskite, oxyborate, vanadate, tungstate, or fluoride crystalfamilies. For example, a crystalline host material for a gain medium mayinclude yttrium aluminum garnet (Y₃Al₅O₁₂, which may be referred to asYAG), yttrium scandium gallium garnet (Y₃Sc₂Ga₃O₁₂, which may bereferred to as YSGG), gadolinium scandium gallium garnet(Gd_(3-x)Sc_(2-y)Ga_(3+x+y)O₁₂, which may be referred to as GSGG),yttrium aluminum perovskite (YAlO₃, which may be referred to as YAP),yttrium aluminum borate (YAl₃(BO₃)₄, which may be referred to as YAB),yttrium orthovanadate (YVO₄), gadolinium orthovanadate (GdVO₄), oryttrium lithium fluoride (LiYF₄, which may be referred to as YLF). As anexample, a gain medium of a solid-state laser may include a YAG crystaldoped with approximately 1.5% Nd, which may be referred to as 1.5 atomic% doping (e.g., approximately 1.5% of the yttrium ions in the YAGcrystal are replaced with neodymium ions).

In particular embodiments, a solid-state laser may include or may bereferred to as a passively Q-switched (PQSW) laser, an activelyQ-switched laser, a Q-switched laser, a diode-pumped solid-state laser(DPSS laser or DPSSL), a microlaser, an optical parametric oscillator(OPO), a self-Raman laser, or any suitable combination thereof. As anexample, a solid-state laser may include a PQSW laser or an activelyQ-switched laser that produces pulses of light at approximately 1030nanometers, approximately 1064 nanometers, or between approximately 1400nanometers and approximately 1480 nanometers. As another example, asolid-state laser may include an OPO that is pumped by a PQSW laser. Asanother example, a solid-state laser may include a self-Raman laser. Inparticular embodiments, a solid-state laser may produce an output beam125 that is a free-space beam. As an example, a solid-state laser maydirectly emit a free-space optical beam that propagates in air, vacuum,water, or glass.

In particular embodiments, a lidar system 100 may include a solid-statelaser configured to emit pulses of light. In particular embodiments, theoptical pulses produced by a solid-state laser may have opticalcharacteristics that include one or more of the following: a pulserepetition frequency of greater than or equal to 20 kHz (e.g.,approximately 20 kHz, 30 kHz, 40 kHz, 60 kHz, 80 kHz, 100 kHz, 120 kHz,150 kHz, 200 kHz, 500 kHz, 1 MHz, or 5 MHz); a pulse duration of lessthan or equal to 20 nanoseconds (e.g., approximately 50 ps, 200 ps, 400ps, 500 ps, 800 ps, 1 ns, 2 ns, 4 ns, 8 ns, 10 ns, 15 ns, or 20 ns); aduty cycle of less than or equal to 1% (e.g., approximately 0.001%,0.005%, 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.5%, or 1%); a pulse energy ofgreater than or equal to 10 nanojoules (e.g., approximately 10 nJ, 50nJ, 100 nJ, 500 nJ, 1 μJ, 2 μJ, 5 μJ, 10 μJ, 20 μJ, or 50 μJ); a peakpulse power of greater than or equal to 1 watt (e.g., approximately 1 W,10 W, 50 W, 100 W, 200 W, 500 W, 1 kW, 2 kW, 10 kW, 50 kW, or 100 kW);an average power of less than or equal to 50 watts (e.g., approximately50 W, 20 W, 10 W, 5 W, 2 W, 1 W, 0.5 W, or 0.1 W); or an operatingwavelength of between 1400 nm and 1700 nm. As an example, a solid-statelaser may produce an output beam 125 with a pulse repetition frequencybetween approximately 40 kHz and approximately 140 kHz, and the pulsesmay have a pulse duration between approximately 100 ps and approximately2 ns. As another example, a solid-state laser may produce pulses with apulse repetition frequency of approximately 100 kHz and a pulse durationof approximately 1 ns, corresponding to a duty cycle of approximately0.01%. (A duty cycle may be determined from a ratio of pulse duration topulse period or from a product of pulse duration and pulse repetitionfrequency.) As another example, a solid-state laser may produce pulseswith a pulse repetition frequency of approximately 500 kHz and a pulseduration of approximately 2 ns, corresponding to a duty cycle ofapproximately 0.1%. As another example, a solid-state laser may producepulses with a pulse duration of approximately 1 ns and a pulse energy ofapproximately 1 μJ, which corresponds to pulses with a peak power ofapproximately 1 kW. (A peak power of a pulse may be determined from aratio of pulse energy to pulse duration). As another example, asolid-state laser may produce pulses with a pulse duration ofapproximately 400 ps and a pulse energy of approximately 5 μJ, whichcorresponds to pulses with a peak power of approximately 12.5 kW. Asanother example, a solid-state laser may produce pulses with a pulseenergy of approximately 4 μJ and a pulse repetition frequency ofapproximately 100 kHz, corresponding to an average power ofapproximately 0.4 W. (An average power may be determined from a productof pulse energy and pulse repetition frequency.) As another example, asolid-state laser may produce pulses with a wavelength of approximately1420 nm, 1440 nm, 1500 nm, 1550 nm, or 1600 nm.

FIG. 10 illustrates an example passively Q-switched (PQSW) laser 400that includes a gain medium 410 and a saturable absorber 420. A PQSWlaser 400 may produce optical pulses through a Q-switching processprovided by an optical interaction between gain medium 410 and saturableabsorber 420. In the example of FIG. 10, the PQSW laser 400 is pumped bypump laser 430, which produces a free-space pump beam 440. The pump beam440 passes through a lens 450 to collimate or focus the pump-beam light,which then propagates to the gain medium 410. In particular embodiments,lens 450 may be referred to as an imaging optic and may include one ormore concave or convex lenses configured to collimate or focus the pumpbeam 440. As an example, lens 450 may focus pump beam 440 to a 1/e² beamdiameter of approximately 100-300 μm in gain medium 410. In particularembodiments, the ends of the laser cavity of the PQSW laser 400 may beformed by back surface 470 and output surface 480.

In particular embodiments, a light source 110 of a lidar system 100 mayinclude a PQSW laser 400 that includes a gain medium 410 and a saturableabsorber 420. As an example, an output beam 460 of a PQSW laser 400 maybe coupled to a splitter or a scanner 120 of a lidar system 100, and atleast part of the output beam 460 may form an output beam 125 of thelidar system 100. As another example, an output beam 460 of a PQSW laser400 may act as a pump source for another optical assembly of a lightsource 110. For example, optical pulses produced by a PQSW laser 400 maybe used to pump an OPO.

A gain medium 410 of a PQSW laser 400 may have any suitable lengthL_(g), any suitable height H, and any suitable width. As an example, again medium 410 may have a length L_(g) of between approximately 1 mmand approximately 30 mm, and a gain medium 410 may have a height H or awidth of between approximately 0.5 mm and approximately 10 mm. Asanother example, a gain medium 410 may include a Yb-doped or Nb-dopedYAG crystal, and the YAG crystal may have a length L_(g) ofapproximately 3.0 mm, a height H of approximately 2.0 mm, and a width ofapproximately 1.5 mm. A saturable absorber 420 may have any suitablelength L_(sa), such as for example, a length of approximately 0.05 mm,0.1 mm, 0.2 mm, 0.3 mm, 0.5 mm, 1 mm, 2 mm, 5 mm, or 10 mm.

In particular embodiments, gain medium 410 of a PQSW laser 400 mayinclude Nd-doped YAG (Nd:YAG), Yb-doped YAG (Yb:YAG), Nd-doped YVO₄(Nd:YVO₄), Nd-doped YSGG (Nd:YSGG), Nd-doped GSGG (Nd:GSGG), Nd-dopedYAP (Nd:YAP), Nd-doped YAB (Nd:YAB), Er-doped YAB (Er:YAB), Nd-doped YLF(Nd:YLF), Er-doped glass (Er:glass), YAB doped with Er and Yb(Er,Yb:YAB), or glass doped with Er and Yb (Er,Yb:glass). As an example,gain medium 410 may include Nd:YAG with 0.5% to 5% Nd doping (e.g., 0.5%to 5% of the yttrium ions in the YAG crystal are replaced with neodymiumions). As another example, gain medium 410 may include Yb:YAG with 2% to20% Yb doping. As another example, gain medium 410 may include Nd:YVO₄with 0.1% to 5% Nd doping.

In particular embodiments, gain medium 410 may be pumped by a pump laser430 that produces a free-space pump beam 440 which is directed into thegain medium 410. Light from the pump beam 440 may be absorbed by opticalgain material (e.g., rare-earth ions) contained within the gain medium410, and the excited gain material may produce optical gain (throughstimulated emission) for particular wavelengths of light circulatingwithin the optical cavity of the PQSW laser 400. The cavity of the PQSWlaser 400 may be formed by back surface 470 and output surface 480. Inparticular embodiments, a pump laser 430 may produce a pump beam 440with any suitable optical power, such as for example, an average opticalpower of greater than or equal to 1 W, 2 W, 5 W, 10 W, 15 W, or 20 W.Additionally, the optical gain material in the gain medium 410 mayabsorb any suitable amount of light from the pump beam 440, such as forexample, greater than or equal to 40%, 50%, 60%, 70%, 80%, 90%, or 95%of the pump-beam light.

In particular embodiments, pump laser 430 may be a laser diode, such asfor example an edge-emitter laser diode, a vertical-cavitysurface-emitting laser (VCSEL) or a vertical-external-cavitysurface-emitting laser (VECSEL). An edge-emitter laser diode may referto a semiconductor laser diode where light propagates in a directionparallel to a surface of the laser's semiconductor substrate, and thelaser light is reflected by or coupled out of the laser diode at acleaved edge. A VCSEL may refer to a semiconductor laser diode wherelight is emitted perpendicular to the semiconductor substrate surface. AVCSEL may include two mirrors (e.g., Bragg reflectors) incorporated intothe VCSEL structure, where the two mirrors are located on either side ofthe VCSEL gain region and form a resonant optical cavity of the VCSEL.Each of the mirrors may be a dielectric mirror (e.g., a mirror formed bythin films of dielectric material deposited onto a surface of the VCSEL)or a semiconductor-based mirror formed by layers of semiconductormaterial having alternating refractive indices. A VECSEL (which may bereferred to as an extended-cavity vertical-cavity surface-emittinglaser, or EC-VCSEL) may refer to a VCSEL-type semiconductor laser diodewith the resonant cavity formed by one mirror incorporated into a VCSELstructure and a second mirror located external to the VCSEL structure.The external mirror may be configured to reflect light at an operatingwavelength of the VECSEL, and the external mirror may act as an outputcoupler from which the pump beam 440 is emitted. The spacing between theVCSEL structure and the external mirror may be any suitable distance,such as for example, approximately 0.01 mm, 0.1 mm, 1 mm, 2 mm, 5 mm, 10mm, 20 mm, or 50 mm. The external mirror of a VECSEL may be a dielectricmirror or a volume Bragg grating (VBG). A VBG may refer to asubstantially transparent substrate which has a periodicrefractive-index variation within its volume (rather than on a surfaceof the substrate), and a VBG may be configured to reflect light at theoperating wavelength of the VECSEL.

In particular embodiments, pump laser 430 may be a VECSEL, and theexternal mirror of the VECSEL may be formed by the back surface 470 ofgain medium 410. As an example, back surface 470 may act as a cavitymirror of the pump laser 430 and as a cavity mirror of the PQSW laser400. For example, back surface 470 may have a dielectric coating with ahigh reflectivity at an operating wavelength of the PQSW laser 400 and apartial reflectivity or high reflectivity at an operating wavelength ofthe pump laser 430. Light emitted by the VECSEL may be directly coupledfrom the VECSEL into the gain medium 410 of the PQSW laser 400. Inparticular embodiments, pump laser 430 may be a VECSEL, and the externalmirror of the VECSEL may be bonded to the back surface 470 of the gainmedium 410. As an example, the external mirror may be attached orcoupled to the back surface 470 by adhesive or epoxy bonding, opticalcontacting, diffusion bonding, chemically activated direct bonding, orany other suitable bonding technique.

In particular embodiments, a pump laser 430 may operate at any suitablewavelength, such as any suitable wavelength between approximately 800 nmand approximately 1000 nm. As an example, the gain medium 410 may bepumped at a wavelength between approximately 800 nm and approximately1000 nm by an edge-emitter laser diode or a VECSEL. As another example,a pump laser 430 may produce light at approximately 808 nm, 888 nm, 908nm, 915 nm, 940 nm, 941 nm, 960 m, 976 nm, or 980 nm. As anotherexample, a pump laser 430 operating at approximately 808-nm may be usedto pump a Nd:YAG crystal, and the PQSW laser 400 may produce an outputbeam 460 with a wavelength of approximately 1064 nm (e.g., 1064.3 nm).As another example, a pump laser 430 operating between approximately 805nm and approximately 811 nm may be used to pump a Nd:YSGG crystal, andthe PQSW laser 400 may produce an output beam 460 with a wavelength ofapproximately 1422.5 nm. As another example, a pump laser 430 operatingbetween approximately 900 nm and approximately 980 nm may be used topump a Yb:YAG crystal, and the PQSW laser 400 may produce an output beam460 with a wavelength of approximately 1030 nm.

In particular embodiments, a pump laser 430 may be temperaturestabilized to stabilize the output wavelength of the pump laser 430. Asan example, a temperature-stabilized pump laser 430 with an 808-nmoutput wavelength may be used to pump a Nd:YAG gain medium 410. Sincethe Nd dopants in a Nd:YAG gain medium 410 have a relatively narrowabsorption band, the 808-nm pump laser 430 may be temperature stabilizedto ensure that the 808-nm output wavelength is maintained (e.g., thepump laser 430 may be temperature stabilized so the output wavelengthvaries by less than or equal to ±3 nm, ±1 nm, ±0.5 nm, or ±0.2 nm). Apump laser 430 may be temperature stabilized using a thermoelectriccooler, a temperature sensor, and a temperature-stabilization circuit,and the pump-laser temperature may be stabilized to within any suitablevalue of a set-point temperature (e.g., within ±10° C., ±5° C., ±1° C.,±0.5° C., or ±0.1° C. of a set-point temperature). In particularembodiments, a pump laser 430 may not require temperature stabilization.As an example, a pump laser 430 with an output wavelength betweenapproximately 940 and approximately 960 nm may be used to pump a Yb:YAGgain medium 410. Since the Yb dopants in a Yb:YAG gain medium have arelatively broad absorption band, the pump laser 430 may not requiretemperature stabilization.

In particular embodiments, pump laser 430 may be a free-space laser(e.g., a laser that directly produces a free-space pump beam 440) or afiber-coupled laser. For a fiber-coupled pump laser 430, the pump laser430 may produce light that is coupled or directed to an optical fiber,and the optical fiber may be terminated by a collimator or lens assemblythat produces a free-space pump beam 440 which is directed to gainmedium 410. In particular embodiments, the gain medium 410 may beside-pumped or end-pumped by the pump laser 430. As an example, for aside-pumping arrangement, the pump beam 440 may enter the gain medium410 through a side surface of the gain medium 410 and may be directedsubstantially orthogonal to the axis along which light propagates withinthe PQSW laser cavity. In the example of FIG. 10, the pump laser 430 isconfigured in an end-pumping arrangement where the pump beam 440 entersthe gain medium 410 through an end surface (e.g., back surface 470) ofthe gain medium 410, and the pump beam 440 propagates along a directionthat is substantially parallel to the propagation axis of light withinthe PQSW laser cavity.

In particular embodiments, PQSW laser 400 may include a saturableabsorber 420. In the example of FIG. 10, gain medium 410 is located onthe pump side of the PQSW laser 400 (e.g., the gain medium 410 isconfigured to receive the pump beam 440), and saturable absorber 420 islocated on the output side of the PQSW laser 400 (e.g., the output beam460 exits the PQSW laser 400 from output surface 480 of the saturableabsorber 420). In particular embodiments, saturable absorber 420 of aPQSW laser 400 may include vanadium-doped YAG (V³⁺:YAG, which may bereferred to as V:YAG), chromium-doped YAG (Cr⁴⁺:YAG, which may bereferred to as Cr:YAG), cobalt-doped zinc selenide (Co²⁺:ZnSe, which maybe referred to as Co:ZnSe), cobalt-doped MgAl₂O₄ (Co²⁺:spinel, which maybe referred to as Co:spinel), neodymium-doped strontium fluoride(Nd²⁺:SrF₂, which may be referred to as Nd:SrF₂), lithium fluoride withF₂ ⁻ color centers (LiF:F₂), glass doped with lead-sulfide (PbS) quantumdots, or a semiconductor saturable absorber mirror (SESAM).

In particular embodiments, saturable absorber 420 may include an opticalmaterial that becomes more optically transparent as the intensity oflight incident on the saturable absorber 420 increases (e.g., theoptical loss of the saturable absorber 420 decreases as incident lightintensity increases). As an example, the dopant vanadium ions in a V:YAGsaturable absorber 420 may absorb light emitted by the gain material ofgain medium 410. This absorption process promotes vanadium ions intoexcited states and depletes the number of ground-state vanadium ionsavailable to absorb additional light emitted by gain medium 410. As thenumber of available vanadium ions in a ground state is depleted, theoptical loss of the V:YAG saturable absorber 420 decreases, whichcorresponds to an increase in optical transmission.

In particular embodiments, for relatively low optical intensities, asaturable absorber 420 may be relatively absorbing (e.g., the saturableabsorber 420 may have a relatively high optical loss), and forrelatively high optical intensities, a saturable absorber 420 may berelatively transparent (e.g., the saturable absorber 420 may have arelatively low optical loss). As an example, when a saturable absorber420 is exposed to an optical intensity of less than or equal to aparticular saturation intensity (e.g., the saturable absorber 420 is ina substantially unsaturated state), the saturable absorber 420 mayabsorb greater than or equal to 10%, 15%, 25%, 50%, 70%, 80%, or 90% ofthe incident light (e.g., the saturable absorber 420 may have atransmission of less than or equal to 90%, 85%, 75%, 50%, 30%, 20%, or10%). When exposed to an optical intensity of greater than or equal tothe saturation intensity (e.g., the saturable absorber 420 issubstantially saturated), a saturable absorber 420 may absorb less thanor equal to 50%, 25%, 10%, 5%, or 1% of the incident light (e.g., thesaturable absorber 420 may have a transmission of greater than or equalto 50%, 75%, 90%, 95%, or 99%).

In particular embodiments, the energy required to saturate a saturableabsorber 420 may depend on the thickness L_(sa) or dopant density of thesaturable-absorber material. A saturable absorber 420 may have anysuitable saturation intensity, such as for example, a saturationintensity of approximately 1 kW/cm², 10 kW/cm², 100 kW/cm², 1 MW/cm², 10MW/cm², or 100 MW/cm². As an example, a V:YAG saturable absorber 420 mayhave a saturation intensity of approximately 3.8 MW/cm². In particularembodiments, a saturable absorber 420 of a PQSW laser 400 may absorblight at a wavelength corresponding to an operating wavelength of thePQSW laser 400. As an example, a V:YAG saturable absorber 420 may havean absorption coefficient (when operating in an unsaturated state) ofapproximately 9.8 cm⁻¹ for a wavelength of approximately 1030 nm. Asanother example, a Cr:YAG saturable absorber 420 may have an unsaturatedabsorption coefficient of approximately 6 cm⁻¹ for a wavelength ofapproximately 1064 nm.

In particular embodiments, a saturable absorber 420 may be referred toas a Q-switch or a passive Q-switch, and the saturable absorber mayallow a PQSW laser 400 to produce optical pulses through a Q-switchingprocess. Q-switching refers to a technique for producing optical pulsesby changing the optical loss (and thus the Q factor, or quality factor)of a laser cavity. The unsaturated optical loss introduced by asaturable absorber 420 corresponds to a reduction in the Q factor of thelaser cavity, and as the saturable absorber 420 saturates, the Q factorincreases (corresponding to a reduction in optical loss). The saturableabsorber 420 acts as a variable attenuator that prevents the PQSW laser400 from lasing when the optical intensity in the laser cavity isrelatively low. As the optical intensity in the laser cavity increases(as a result of the pump beam 440 exciting the gain material of gainmedium 410), the saturable absorber 420 saturates and becomes moretransparent (e.g., the optical-cavity loss decreases), and at aparticular point after the optical-cavity gain exceeds the loss, thePQSW laser 400 emits an optical pulse. After the pulse is emitted, thesaturable absorber 420 returns to an unsaturated state (with relativelyhigh optical loss), and the Q-switching process repeats periodically,resulting in the PQSW laser 400 emitting an output beam 460 thatincludes a series of Q-switched optical pulses.

In particular embodiments, a Q-switched laser may be passivelyQ-switched or actively Q-switched. A passively Q-switched laser mayinclude a passive Q-switch (e.g., saturable absorber 420), and anactively Q-switched laser may include an active Q-switch, such as forexample, an acousto-optic modulator (AOM) or an electro-optic modulator(EOM). An active Q-switch, which may take the place of a passiveQ-switch, may refer to an electrically driven device that providescontrollable optical loss in a laser cavity. As an example, an activelyQ-switched laser may include a gain medium 410 (e.g., Nd:YAG) pumped bya pump laser 430 and an AOM that acts as an active Q-switch.

In particular embodiments, saturable absorber 420 may be bonded to gainmedium 410. Saturable absorber 420 and gain medium 410 being bondedtogether may refer to saturable absorber 420 and gain medium 410 beingmechanically attached or coupled together by adhesive or epoxy bonding,by a direct-bonding technique (e.g., optical contacting, diffusionbonding, or chemically activated direct bonding), or by any othersuitable bonding technique. Adhesive or epoxy bonding may includeattachment using a substantially transparent adhesive or epoxy, such asfor example, an optically clear adhesive or an ultraviolet (UV)light-curing adhesive. Optical contacting may include joining togethertwo optical-quality surfaces (e.g., two polished surfaces substantiallyfree of contaminants) so that the surfaces are held together byintermolecular forces. Diffusion bonding may include applying heat orpressure to the saturable absorber 420 and gain medium 410 to allowelements to diffuse between the two parts and form a bond at the atomiclevel. In chemically activated direct bonding, two surfaces arechemically activated to create dangling bonds. The activated surfacesare pre-bonded together through hydrogen bonds, and the two pre-bondedparts are then annealed to form covalent bonds.

In particular embodiments, a PQSW laser 400 may include an interface 490located between the gain medium 410 and saturable absorber 420. Aninterface 490 may represent a bond, border, or coating located betweengain medium 410 and saturable absorber 420. The thickness of interface490 may be any suitable value between zero thickness and approximately1-mm thickness. As an example, an optical or diffusion bond may have athickness close to or approximately equal to zero (e.g., the thicknessmay be less than or equal to 1 μm, 100 nm, 10 nm, or 1 nm). As anotherexample, interface 490 may include adhesive or epoxy material and mayhave a thickness of approximately 0.1-100 μm.

In particular embodiments, gain medium 410 may include Nd:YAG, Yb:YAG,Nd:YVO₄, Nd:YSGG, Nd:GSGG, Nd:YAP, Nd:YAB, Er:YAB, Nd:YLF, Er:glass,Er,Yb:YAB, or Er,Yb:glass, and saturable absorber 420 may include V:YAG,Cr:YAG, Co:spinel, Nd:SrF₂, or LiF:F₂. As an example, PQSW laser 400 mayinclude a Nd:YAG gain medium 410 bonded to a Cr:YAG saturable absorber420. As another example, PQSW laser 400 may include a Nd:YAG gain medium410 bonded to a V:YAG saturable absorber 420. As another example, PQSWlaser 400 may include a Yb:YAG gain medium 410 bonded to a V:YAGsaturable absorber 420. In particular embodiments, gain medium 410 andsaturable absorber 420 may each be part of a monolithic structure in asingle host crystal. As an example, PQSW laser 400 may include a singleYAG crystal with part of the crystal doped with Nd or Yb (to form gainmedium 410) and another part of the crystal doped with Cr or V (to formsaturable absorber 420). The interface 490 may represent a border ortransition region between the gain medium 410 and the saturable absorber420, and the interface 490 may have a thickness close to orapproximately equal to zero.

In particular embodiments, interface 490 may include a thin-filmdielectric coating configured to block or reflect light from the pumpbeam 440. As an example, interface 490 may include a dielectric coatingwith a high reflectivity at an operating wavelength of the pump laser430 (e.g., a reflectivity of greater than or equal to 70%, 80%, 90%,95%, or 99% at the pump-laser wavelength). Additionally, the dielectriccoating may have a low reflectivity at an operating wavelength of thePQSW laser 400 (e.g., a reflectivity of less than or equal to 20%, 10%,5%, 1%, or 0.1% at the PQSW-laser wavelength). When light from the pumpbeam 440 enters the gain medium 410, the light is absorbed by the gainmaterial. After propagating through the gain medium 410, any residual,unabsorbed pump light may enter the saturable absorber 420 and may causeunwanted bleaching or saturation of the saturable absorber 420. Having ahigh-reflectivity coating at the pump-laser wavelength may prevent mostof the residual pump-beam light from entering the saturable absorber420. Most of the pump-beam light may be reflected by the dielectriccoating located at the interface 490, and the reflected pump-beam lightmay propagate back through the gain medium 410.

In particular embodiments, the length L_(g) or the dopant density ofgain medium 410 may be sufficient so that only a fraction of light frompump beam 440 reaches interface 490 (e.g., most of the pump beam 440 isabsorbed by the gain material of gain medium 410 during the first passof pump beam 440 through gain medium 410). As an example, less than orequal to 40%, 20%, 10%, 5%, or 1% of pump beam 440 that is incident onback surface 470 of gain medium 410 may reach the interface 490. Inparticular embodiments, a dielectric coating located at interface 490 toblock or reflect light from the pump beam 440 may not be necessary ifthe absorption of the pump beam 440 in gain medium 410 is greater than aparticular amount (e.g., if greater than or equal to 60%, 80%, 90%, 95%,or 99% of the pump beam 440 is absorbed in the gain medium 410 duringits first pass through the gain medium 410). In particular embodiments,a dielectric coating located at interface 490 to block or reflect lightfrom the pump beam 440 may not be necessary if the saturation intensityof the saturable absorber 420 is greater than the intensity of theresidual pump-beam light that reaches the saturable absorber 420. As anexample, a V:YAG saturable absorber 420 with a 3.8 MW/cm² saturationintensity may not require a dielectric coating at interface 490 to blockor reflect light from the pump beam 440.

In particular embodiments, back surface 470 and output surface 480 ofPQSW laser 400 may form two ends of a laser cavity of the PQSW laser400. The gain medium 410 and saturable absorber 420 may be locatedbetween the back surface 470 and output surface 480 so that the gainmedium 410 and saturable absorber 420 are contained within the lasercavity. In particular embodiments, a laser cavity may be referred to asa resonant cavity, resonator cavity, optical resonator, optical cavity,or cavity. In particular embodiments, a back surface 470 may form oneend of a laser cavity and may be referred to as an input surface, aninput coupler, an end surface, a cavity surface, a laser-cavity surface,or a laser-cavity mirror. A back surface 470 may refer to a surfacethrough which pump beam 440 is received or a surface which has a highreflectivity for an operating wavelength of the PQSW laser 400. Inparticular embodiments, an output surface 480 may form another end of alaser cavity and may be referred to as an output coupler, an endsurface, a cavity surface, a laser-cavity surface, or a laser-cavitymirror. An output surface 480 may refer to a surface from which theoutput beam 460 is emitted.

In particular embodiments, gain medium 410 may include a back surface470 with a dielectric coating. As an example, back surface 470 may havea coating with a low reflectivity (e.g., R<10%) at a pump-laserwavelength and a high reflectivity (e.g., R>90%) at an operatingwavelength of the PQSW laser 400. In particular embodiments, saturableabsorber 420 may include an output surface 480 with a dielectriccoating. In particular embodiments, a dielectric coating (which may bereferred to as a thin-film coating, interference coating, or coating)may include one or more layers of dielectric materials (e.g., SiO₂,TiO₂, Al₂O₃, Ta₂O₅, MgF₂, LaF₃, or AlF₃) having particular thicknesses(e.g., thickness less than 1 μm) and particular refractive indices. Adielectric coating may be deposited onto a surface (e.g., a surface ofgain medium 410 or saturable absorber 420) using any suitable depositiontechnique, such as for example, sputtering or electron-beam deposition.

In particular embodiments, a high-reflectivity dielectric coating may bereferred to as an HR coating and may have any suitable reflectivity(e.g., a reflectivity R greater than or equal to 80%, 90%, 95%, 99%,99.5%, or 99.9%) at any suitable wavelength. As an example, back surface470 have may an HR coating at an operating wavelength of a PQSW laser400 (e.g., R>99.8% at 1030 nm, 1064 nm, or 1422.5 nm). As anotherexample, interface 490 may have an HR coating at a pump-laser wavelength(e.g., R>99% at 800-820 nm or 920-980 nm).

In particular embodiments, a low-reflectivity dielectric coating may bereferred to as a high-transmission (HT) coating or an anti-reflection(AR) coating and may have any suitable reflectivity (e.g., R less thanor equal to 10%, 5%, 2%, 1%, 0.5%, or 0.2%) at any suitable wavelength.As an example, back surface 470 may have an HT coating at a pump-laserwavelength (e.g., R<5% at 800-820 nm or 920-980 nm). As another example,output surface 480 may have an HT coating at a pump-laser wavelength(e.g., R<5% at 800-820 nm or 920-980 nm). As another example, interface490 may have an AR coating at an operating wavelength of a PQSW laser400 (e.g., R<0.2% at 1030 nm, 1064 nm, or 1422.5 nm).

In particular embodiments, a dielectric coating with an intermediate orpartial reflectivity may be referred to as a partially reflective (PR)coating and may have any suitable reflectivity (e.g., R betweenapproximately 10% and approximately 90%) at any suitable wavelength. Asan example, output surface 480 may have a PR coating at an operatingwavelength of a PQSW laser 400 (e.g., R approximately equal to 50% at1030 nm, 1064 nm, or 1422.5 nm).

In particular embodiments, a dielectric coating may be a dichroiccoating which has a particular type of reflectivity (e.g., HR, HT, AR,or PR) at particular wavelengths. As an example, back surface 470 mayhave a dielectric coating which is HR (e.g., R greater than 99.8%) at anoperating wavelength of a PQSW laser 400 (e.g., at 1030 nm, 1064 nm, or1422.5 nm) and HT (e.g., R less than 5%) at a pump-laser wavelength(e.g., at 800-820 nm or 920-980 nm). As another example, output surface480 may have a dielectric coating which is PR (e.g., R is approximatelyequal to 50%) at an operating wavelength of a PQSW laser 400 (e.g., at1030 nm, 1064 nm, or 1422.5 nm) and HT (e.g., R less than 5%) at apump-laser wavelength (e.g., at 800-820 nm or 920-980 nm). As anotherexample, interface 490 may have a dielectric coating which is AR (e.g.,R<0.5%) at an operating wavelength of a PQSW laser 400 (e.g., at 1030nm, 1064 nm, or 1422.5 nm) and HR (e.g., R>99%) at a pump-laserwavelength (e.g., 800-820 nm or 920-980 nm).

In particular embodiments, a PQSW laser 400 may be configured to operateat any suitable wavelength, such as for example, a wavelength ofapproximately 1030 nm, approximately 1064 nm, or between approximately1400 nm and approximately 1480 nm. In particular embodiments, a PQSWlaser 400 may generate optical pulses at a wavelength less than 1400 nm(e.g., approximately 1030 nm or 1064 nm), and these optical pulses maybe used as a pump source for another laser or for an OPO. As an example,a PQSW laser 400 with a Nd:YAG gain medium 410 and a Cr:YAG or V:YAGsaturable absorber 420 may produce an output beam 460 with opticalpulses having a wavelength of approximately 1064 nm (e.g., the operatingwavelength of the PQSW laser 400 is approximately 1064 nm), a pulseenergy of greater than or equal to 10 μJ, a pulse repetition frequencyof greater than or equal to 60 kHz, or a pulse duration of less than orequal to 2 ns. A Nd:YAG/Cr:YAG or Nd:YAG/V:YAG PQSW laser 400 may bepumped by an edge-emitter pump laser 430 with an operating wavelength of800-820 nm (e.g., approximately 808 nm) and an output power of greaterthan or equal to 8 W. The Nd:YAG gain medium 410 may have a length L_(g)of approximately 2-5 mm and a dopant density of approximately 1.5% Nd. ACr:YAG saturable absorber 420 may have a length L_(sa) of approximately0.1-1 mm. As another example, a PQSW laser 400 with a Yb:YAG gain medium410 and a Cr:YAG or V:YAG saturable absorber 420 may have an operatingwavelength of approximately 1030 nm and may produce optical pulses witha pulse energy of greater than or equal to 10 μJ, a pulse repetitionfrequency of greater than or equal to 60 kHz, or a pulse duration ofless than or equal to 2 ns. The Yb:YAG/Cr:YAG or Yb:YAG/V:YAG PQSW laser400 may be pumped at a wavelength of 920-980 nm (e.g., approximately 976nm). For example, the pump laser 430 may be a VECSEL with an outputpower of greater than or equal to 2 W. The Yb:YAG gain medium 410 mayhave a length L_(g) of approximately 2-5 mm and a dopant density ofapproximately 10% Yb. A V:YAG saturable absorber 420 may have a lengthL_(sa) of approximately 0.1-1 mm).

In particular embodiments, a PQSW laser 400 may directly generateoptical pulses at a wavelength between approximately 1400 nm andapproximately 1600 nm, and the optical pulses may be used to performlidar measurements. As an example, a PQSW laser 400 with a Nd:YSGG gainmedium 410 may have an operating wavelength of approximately 1422.5 nm.A Nd:YSGG gain medium 410 may have a Nd-doping density of approximately0.5% to 5% (e.g., 1.9% Nd dopant density) and a length L_(g) ofapproximately 2-5 mm. The Nd:YSGG gain medium 410 may be pumped by aVECSEL pump laser 430 with an operating wavelength of approximately806-811 nm, and the Nd:YSGG gain medium 410 may absorb greater than orequal to 70% of the incident pump beam 440. The PQSW laser 400 mayinclude a V:YAG saturable absorber 420 with a length L_(sa) ofapproximately 1-5 mm. A Nd:YSGG/V:YAG PQSW laser 400 may produce opticalpulses with a pulse energy of greater than or equal to 1 μJ, a pulserepetition frequency of greater than or equal to 60 kHz, or a pulseduration of less than or equal to 2 ns. As another example, a PQSW laser400 may include a Nd:GSGG, Nd:YAP, or Nd:YAG gain medium 410 and mayoperate at a wavelength of approximately 1422.5 nm, 1432.8 nm, or 1443.8nm, respectively.

In particular embodiments, a PQSW laser 400 may include a Er,Yb:YAB gainmedium 410. The Er,Yb:YAB gain medium 410 may be pumped by a pump laser430 with an operating wavelength of approximately 940 nm orapproximately 976 nm. The PQSW laser 400 may include a Co:spinelsaturable absorber 420, a nanoparticle-based saturable absorber 420, orany other suitable saturable absorber 420, and the PQSW laser 400 mayproduce output pulses with a wavelength of approximately 1535 nm.

FIG. 11 illustrates an example passively Q-switched laser 400 thatincludes an end cap 500. In particular embodiments, the end surfaces ofa laser cavity of a PQSW laser 400 may be formed by back surface 470 andoutput surface 480, and end cap 500, gain medium 410, and saturableabsorber 420 may be located within the laser cavity and between thelaser-cavity end surfaces. In particular embodiments, end cap 500 mayface pump laser 430. In the example of FIG. 11, end cap 500 ispositioned to receive pump beam 440 so that pump beam 440 propagatesthrough the end cap 500 before entering gain medium 410. In particularembodiments, end cap 500 may act as a heat spreader that reducesthermally induced stress or thermally induced lensing within gain medium410. In particular embodiments, an end cap 500 may include back surface470. A back surface 470 that is part of end cap 500 may be similar to aback surface 470 that is part of gain medium 410 (e.g., back surface 470of end cap 500 may include a dielectric coating with particularreflectivity at particular wavelengths). In particular embodiments, anend cap 500 may have a length L_(ec) of approximately 0.5-3 mm, and gainmedium 410 may have a length L_(g) of approximately 2-5 mm. As anexample, an end cap 500 may have a length L_(ec) of approximately 1 mm,and gain medium 410 may have length L_(g) of approximately 3-4 mm.

In particular embodiments, an end cap 500 may refer to an undoped hostmaterial that is bonded to gain medium 410 (e.g., end cap 500 and gainmedium 410 may be bonded together by adhesive or epoxy or by adirect-bonding technique). An end cap 500 may correspond to a gainmedium 410 without the presence of gain-material dopants (e.g., the endcap 500 is substantially free of gain-material dopants) or with a lowconcentration of gain-material dopants. As an example, an end cap 500may include a separate piece of undoped YAG crystal (e.g., a YAG crystalthat is substantially free of gain-material dopants) that is bonded to aNd:YAG gain medium 410. As another example, an end cap 500 may be anundoped YSGG crystal that is bonded to a Nd:YSGG gain medium 410. Inparticular embodiments, an end cap 500 being substantially free ofgain-material dopants may refer to an end cap 500 with less than aparticular amount (e.g., less than approximately 1%, 0.1%, 0.01%, or0.001%) of the concentration of dopants in a gain medium 410. As anexample, if a gain medium 410 is doped with 1.5% Nd and an end cap 500has less than 1% of the dopant density of the gain medium 410, then theend cap 500 may have a Nd dopant density of less than or equal to0.015%. In particular embodiments, an end cap 500 having a lowconcentration of gain-material dopants may refer to an end cap 500 withless than a particular amount (e.g., less than approximately 20%, 10%,5%, or 2%) of the concentration of dopants in a gain medium 410. Inparticular embodiments, an end cap 500 may be integrated into or may bepart of a host crystal of gain medium 410. As an example, a single hostcrystal (e.g., YAG) may include both gain medium 410 (e.g., Nd:YAG) andend cap 500 (e.g., undoped YAG). As another example, a single YAG hostcrystal with an overall length L_(ec)+L_(g) may be doped with Nd ions orCr ions over a length L_(g), and the remaining L_(ec) portion may be anundoped end cap 500 that is substantially free of Nd or Cr dopants. Asanother example, a single YAG host crystal may have a 5-mm overalllength where the first 1-mm is an undoped YAG end cap 500, and theremaining 4-mm is 1.5% Nd-doped YAG. As another example, a single YSGGhost crystal may have a length L_(g) that includes Nd dopants and alength L_(ec) that is substantially free of Nd dopants.

FIG. 12 illustrates an example passively Q-switched laser 400 thatincludes an air gap 510 between the gain medium 410 and the saturableabsorber 420. In particular embodiments, gain medium 410 and saturableabsorber 420 may be discrete optical elements which are separated by airgap 510. An air gap 510 may have any suitable length L_(air) betweenapproximately 0 mm and approximately 50 mm. As an example, air gap 510may have a length L_(air) of approximately 0.1 mm, 0.5 mm, 1 mm, 2 mm, 3mm, 5 mm, 10 mm, 15 mm, 20 mm, or 50 mm. In the example of FIG. 12, theend surfaces of a laser cavity of the PQSW laser 400 are formed by backsurface 470 and output surface 480, and gain medium 410, surface A, airgap 510, surface B, and saturable absorber 420 are located within thelaser cavity and between the laser-cavity end surfaces. In particularembodiments, surface A and surface B may each include a dielectriccoating with a particular reflectivity (e.g., HR, HT, AR, or PR) atparticular wavelengths. As an example, surface A may have a coating thatis HR (e.g., R>95%) at a pump-laser wavelength and AR (e.g., R<0.5%) atan operating wavelength of the PQSW laser 400. The HR coating mayreflect most pump-laser light that is incident on surface A, and the ARcoating may allow most of the PQSW laser light to pass through surfaceA. As another example, surface B may have an AR coating at an operatingwavelength of the PQSW laser 400.

FIG. 13 illustrates an example optical parametric oscillator (OPO) 600configured to operate in an idler-resonant mode. In particularembodiments, an OPO 600 may refer to a light source that produces lightfrom a parametric-amplification process in an OPO medium 610. An OPO 600may include an OPO medium 610, and the OPO medium 610 may be referred toas a nonlinear optical crystal or a nonlinear crystal. An OPO 600 mayconvert pulses of input light (which may be referred to as pump light,OPO pump light, or OPO pump) supplied by a pump laser (e.g., a PQSWlaser 400 or an actively Q-switched laser) into two longer wavelengthsof light (signal and idler) by means of a nonlinear-optical interactionin the OPO medium 610. In particular embodiments, an OPO 600 may receiveOPO pump light from any suitable pulsed laser source, such as forexample, a PQSW laser 400 or an actively Q-switched laser. The OPOmedium 610 may convert at least part of the received pump pulses intolonger-wavelength signal pulses and idler pulses. Additionally, the OPO600 or OPO medium 610 may emit at least a portion of the signal pulses(e.g., the emitted signal pulses may correspond to an output beam 125).

In particular embodiments, a light source 110 of a lidar system 100 mayinclude a solid-state laser, where the solid-state laser includes a PQSWlaser 400 and an OPO 600. As an example, light source 110 may include anOPO 600 pumped by pulses of light from a Nd:YAG/Cr:YAG PQSW laser 400, aNd:YAG/V:YAG PQSW laser 400, a Yb:YAG/Cr:YAG PQSW laser 400, or aYb:YAG/V:YAG PQSW laser 400. In particular embodiments, pulses of OPOpump light may correspond to the pulses of light of output beam 460produced by PQSW laser 400. As an example, the OPO pump beam illustratedin each of FIGS. 13-15 may correspond to an output beam 460 of PQSWlaser 400.

The light produced by an OPO 600 at two longer wavelengths may bereferred to as the signal and idler, where the wavelength of the signalis shorter than the wavelength of the idler. The pump, signal, and idlerwavelengths (λ_(p), λ_(s), and λ_(i), respectively) may satisfy therelationship ¼=λ_(p)+¼ where λ_(p) is less than λ_(s) and λ_(i), and isless than λ_(s). As an example, for a 1030-nm OPO pump wavelength(corresponding to an operating wavelength of a Yb:YAG PQSW laser 400),the signal and idler wavelengths may be approximately 1533.8 nm and3135.8 nm, respectively. As another example, for a Nd:YAG PQSW laser 400that produces a 1064.3-nm OPO pump wavelength, the signal and idlerwavelengths may be approximately 1544.8 nm and 3421.7 nm, respectively.As another example, for a Yb:YAG PQSW laser 400 that produces a 1030-nmOPO pump wavelength, the signal and idler wavelengths may beapproximately 1473.6 nm and 3421.7 nm, respectively.

In particular embodiments, the OPO pump pulses from PQSW laser 400 mayhave a pulse energy of greater than or equal to 10 μJ, a pulse durationof less than or equal to 2 ns, a 50-500 kHz repetition rate, or awavelength of 1000-1200 nm (e.g., a wavelength of approximately 1030 nmor approximately 1064 nm (e.g., 1064.3 nm)). Additionally, an OPO pumpbeam may have a 1/e² beam diameter of between approximately 100 μm andapproximately 300 μm. In particular embodiments, each optical pulse froma PQSW laser 400 that pumps OPO medium 610 may result in the productionof a corresponding signal pulse and idler pulse. As an example, an OPO600 that is pumped by a PQSW laser 400 that produces pulses with aparticular repetition rate (e.g., 50-500 kHz) may produce output signalpulses at approximately the same repetition rate. Signal pulses emittedby an OPO 600 may have a pulse energy of greater than or equal to 1 μJ,a pulse duration of less than or equal to 2 ns, a 50-500 kHz repetitionrate, or a wavelength between approximately 1400 nm and approximately1600 nm. Output signal pulses produced by an OPO 600 may form an outputbeam 125 which may be sent to a splitter or a scanner 120 of a lidarsystem 100 and then scanned across a FOR of the lidar system 100.

In particular embodiments, OPO 600 may include an OPO medium 610 whichis a periodically poled crystal material, such as for example,periodically poled potassium titanyl phosphate (PPKTP), periodicallypoled potassium titanyl arsenate (PPKTA), periodically poled rubidiumtitanyl arsenate (PPRTA), periodically poled lithium niobate (PPLN),periodically poled lithium tantalate (PPLT), or periodically poledstoichiometric lithium tantalate (PPSLT). A periodically poled crystalmaterial may refer to a crystal material (e.g., titanyl phosphate, orKTP) which undergoes a periodic-poling process that produces a spatiallyperiodic reversal of the orientation of the ferroelectric domains in thecrystal. A periodically poled crystal material may exhibit improvedconversion of pump light into signal and idler light by ensuring thatthe pump, signal, and idler are quasi-phase matched in the OPO medium610. The periodic poling may be applied along a propagation axis of theOPO medium 610 so that the poled domains are oriented approximatelyparallel to the back surface 620 or output surface 630. In the exampleof FIGS. 13-15, the domains are indicated by vertical lines within theOPO medium 610. In particular embodiments, an OPO medium 610 may havebetween approximately 100 and 500 domains. The period of the domains maybe any suitable distance between approximately 10 μm and approximately50 μm. As an example, a PPKTP OPO medium 610 may have a domain period ofapproximately 20 μm, 25 μm, 30 μm, 35 μm, or 40 μm.

In particular embodiments, an OPO medium 610 of an OPO 600 may beconfigured to produce signal light at a wavelength between approximately1400 nm and approximately 1600 nm. As an example, an OPO 600 may producesignal light with a wavelength between approximately 1520 nm andapproximately 1574 nm. As another example, an OPO 600 with a PPKTP OPOmedium 610 may produce signal light at a wavelength of approximately1474 nm, approximately 1534 nm, or approximately 1545 nm. In particularembodiments, a length of OPO medium 610 (e.g., a distance between backsurface 620 and output surface 630) may be any suitable value betweenapproximately 1 mm and approximately 100 mm. As an example, OPO medium610 may have a length of approximately 5 mm, 10 mm, 15 mm, 20 mm, or 25mm.

In particular embodiments, OPO 600 may include a temperature-controlledenclosure (e.g., an oven, a heater, or a thermoelectric-cooler device)that provides temperature stabilization for OPO medium 610. As anexample, an OPO medium 610 may be maintained at any suitabletemperature, such as for example, a temperature of approximately 25° C.,50° C., 75° C., or 100° C. The temperature of an OPO medium 610 may bestabilized to within any suitable value of a set-point temperature(e.g., within ±2° C., ±1° C., ±0.5° C., ±0.1° C., or ±0.05° C. of aset-point temperature). As another example, a PPKTP OPO medium 610 witha 35-micron to 38-micron domain period may be operated at a temperaturebetween approximately 27° C. and 127° C. and may be configured toproduce a signal wavelength from approximately 1520 nm (at 27° C.) toapproximately 1574 nm (at 127° C.). As another example, a PPKTP OPOmedium 610 with a 36.5-micron domain period may be stabilized at aset-point temperature of 75-80° C. to produce a signal wavelength ofapproximately 1533.8 nm when pumped by a Yb:YAG PQSW laser 400 operatingat approximately 1030 nm. As another example, a PPKTP OPO medium 610with a 36.5-micron domain period may be operated at 75-80° C. to producea signal wavelength of approximately 1544.8 nm when pumped by a Nd:YAGPQSW laser 400 operating at approximately 1064.3 nm.

In particular embodiments, an OPO medium 610 of an OPO 600 may include aback surface 620 with a dielectric coating. As an example, a backsurface 620 may have a coating with a relatively low reflectivity for apump wavelength (e.g., a wavelength of the PQSW laser 400 providing theOPO pump light) and a relatively high reflectivity for a signalwavelength of the OPO 600. Additionally back-surface coating may be highreflectivity or low reflectivity for an idler wavelength of the OPO 600.In particular embodiments, an OPO medium 610 of an OPO 600 may includean output surface 630 with a dielectric coating. As an example, anoutput surface 630 may have a coating with a relatively highreflectivity for OPO pump light and a relatively low or partialreflectivity for a signal wavelength of the OPO 600. Additionally, theoutput-surface coating may be high reflectivity or low reflectivity foran idler wavelength of the OPO 600. In particular embodiments, an OPO600 may include an optical resonator. As an example, an opticalresonator of an OPO 600 may be formed by back surface 620 and outputsurface 630. The OPO 600 illustrated in FIG. 13 may be referred to as anidler-resonant OPO since an optical resonator for the idler wavelengthis formed by back surface 620 and output surface 630, both of which haveHR coatings for the idler wavelength.

In the example of FIG. 13, OPO medium 610 has a back surface 620 with acoating that is AR for a pump wavelength (e.g., R<2% at an operatingwavelength of the PQSW laser 400), HR (e.g., R>90%) for a signalwavelength, and HR (e.g., R>90%) for an idler wavelength. Additionally,the output surface 630 has a coating that is HR for a pump wavelength,AR for a signal wavelength, and HR for an idler wavelength. As anexample, the back surface 620 in FIG. 13 may have a coating with thefollowing reflectivity values: R<0.5% at approximately 1030 nm or 1064nm (corresponding to a pump wavelength); R>98% at approximately 1534 nmor 1544 nm (corresponding to a signal wavelength); and R>95% atapproximately 3136 nm or 3422 nm (corresponding to an idler wavelength).As another example, the output surface 630 in FIG. 13 may have a coatingwith the following reflectivity values: R>98% at approximately 1030 nmor 1064 nm; R<0.5% at approximately 1534 nm or 1544 nm; and R>95% atapproximately 3136 nm or 3422 nm. A pump-AR coating on back surface 620may allow most of the OPO pump light to pass into OPO medium 610 withminimal reflection of the OPO pump light. The pump-HR coating on outputsurface 630 may reflect most of the OPO pump light that reaches theoutput surface 630 so that the OPO pump light makes two passes throughthe OPO gain medium 610. This double-pass arrangement for the OPO pumplight may improve the efficiency of converting pump light into signaland idler light. Additionally, the pump-HR coating on the output surface630 may substantially block the OPO pump light from exiting the OPOmedium 610 along with the signal beam. The signal-HR coating on backsurface 620 reflects signal light so that most of the signal lightgenerated in the OPO medium 610 is emitted from output surface 630,which is AR-coated for the signal.

FIG. 14 illustrates an example optical parametric oscillator 600configured to operate in a signal-resonant mode. In the example of FIG.14, OPO medium 610 has a back surface 620 with a coating that is AR fora pump wavelength (e.g., R<2% at an operating wavelength of the PQSWlaser 400), HR (e.g., R>90%) for a signal wavelength, and AR (e.g.,R<2%) for an idler wavelength. Additionally, the output surface 630 hasa coating that is HR for a pump wavelength, PR for a signal wavelength,and AR for an idler wavelength. As an example, at a signal wavelength,the output surface 630 may have a PR coating with a reflectivity betweenapproximately 10% and approximately 90% (e.g., a reflectivity ofapproximately 20%, 30%, 40%, 50%, 60%, 70%, or 80%). As another example,the back surface 620 in FIG. 14 may have a coating with the followingreflectivity values: R<0.5% at approximately 1030 nm or 1064 nm; R>98%at approximately 1534 nm or 1544 nm; and R<2% at approximately 3136 nmor 3422 nm. As another example, the output surface 630 in FIG. 14 mayhave a coating with the following reflectivity values: R>98% atapproximately 1030 nm or 1064 nm; R 50% at approximately 1534 nm or 1544nm; and R<2% at approximately 3136 nm or 3422 nm. The OPO 600illustrated in FIG. 14 may be referred to as a signal-resonant OPO sincean optical resonator for the signal wavelength is formed by thesignal-HR coating on the back surface 620 and the signal-PR coating onthe output surface 630.

In particular embodiments, an OPO 600 may be configured to be resonantfor both the signal and idler. As an example, back surface 620 may havea coating that is AR for a pump wavelength, HR for a signal wavelength,and HR for an idler wavelength. The output surface 630 may have acoating that is HR for a pump wavelength, PR for a signal wavelength,and HR for an idler wavelength.

In particular embodiments, pump, signal, or idler beams may travel alonga common optical axis (e.g., the pump, signal, or idler beams may not bedisplaced from one another along a transverse direction). For clarity ofidentifying the beams in the examples of FIGS. 14-15, the pump, signal,or idler beams are illustrated as being offset from one another along atransverse direction. In FIG. 14, the idler and signal beams emittedfrom output surface 630 may be coaxial, and similarly, in FIGS. 14 and15, the idler and pump beams on the back-surface side of the OPO medium610 may be coaxial. In particular embodiments, light from a pump oridler beam that is emitted by OPO medium 610 may be absorbed, reflected,or dispersed by a surface of an optical element (e.g., a lens, window,or filter). In FIG. 14, the idler beam emitted from output surface 630(along with the signal beam) may be reflected or absorbed by a coatingon a surface of OPO 600 (e.g., a coating on an output window of the OPO600) or a coating located downstream from the OPO 600. In FIGS. 14 and15, the idler beam emitted toward the PQSW laser 400 may be reflected orabsorbed by a coating on an imaging optic of the PQSW laser 400 or maybe spatially dispersed by the curvature of an imaging optic.

FIG. 15 illustrates an example optical parametric oscillator 600configured to operate in a cross-resonant mode. In the example of FIG.15, OPO medium 610 has a back surface 620 with a coating that is AR fora pump wavelength (e.g., R<2% at an operating wavelength of the PQSWlaser 400), HR (e.g., R>90%) for a signal wavelength, and AR (e.g.,R<2%) for an idler wavelength. Additionally, the output surface 630 hasa coating that is HR for a pump wavelength, AR for a signal wavelength,and HR for an idler wavelength. For each of the signal and idlerwavelengths, a cross-resonant OPO 600 (which may be referred to as apartially resonant OPO 600) may have one surface with an HR coating andanother surface with an AR coating. In FIG. 15, for the signalwavelength, back surface 620 is HR, and output surface 630 is AR. Forthe idler wavelength, back surface 620 is AR, and output surface 630 isHR.

In particular embodiments, a cross-resonant OPO 600 may be operated asan idler-resonant OPO 600 or a signal-resonant OPO 600 with the additionof an external mirror. As an example, a cross-resonant OPO 600 may beconfigured to operate as an idler-resonant OPO by adding an externalmirror that reflects the idler wavelength. An optical resonator for theidler may be formed by output surface 630 and an idler-HR surface of theexternal mirror. As another example, a cross-resonant OPO 600 may beconfigured to operate as a signal-resonant OPO by adding an externalmirror that reflects at least part of the signal wavelength. An opticalresonator for the signal may be formed by back surface 620 and asignal-HR or signal-PR surface of the external mirror. An externalmirror may have a reflective surface that is curved (e.g., concave orconvex) or flat and may have an HR or PR coating for the signal oridler. Additionally, an external mirror may be positioned any suitabledistance from the back surface 620 or the output surface 630 (e.g., adistance of approximately 0.5 mm, 1 mm, 2 mm, 3 mm, 5 mm, 10 mm, or 20mm from the back surface 620 or output surface 630).

FIG. 16 illustrates an example idler-resonant optical parametricoscillator 600 with an external mirror M1. The OPO in FIG. 16corresponds to the cross-resonant OPO in FIG. 15 with the addition ofexternal mirror M1. The external mirror M1 is positioned between theOPO-pump source (e.g., PQSW laser 400) and the OPO medium 610. Mirror M1has surface S1 facing back surface 620, and surface S1 has a coatingwhich is AR for the pump wavelength and HR for the idler wavelength. Theidler-HR coating is configured to reflect most of the idler beam backinto the OPO medium 610. By adding the high reflecting surface S1 forthe idler wavelength, a cross-resonant OPO may be converted into anidler-resonant OPO with an external mirror M1. Additionally, externalmirror M1 may include a pump-AR coating to allow the OPO pump beam topass through the external mirror M1 with minimal absorption orreflection.

FIG. 17 illustrates an example signal-resonant optical parametricoscillator 600 with an external mirror M2. The OPO in FIG. 17corresponds to the cross-resonant OPO in FIG. 15 with the addition ofexternal mirror M2. The external mirror M2 has surface S2 facing outputsurface 630, and surface S2 may have a coating which is HR or PR for thesignal wavelength. The external mirror M2 may be configured to receivethe signal beam emitted by the OPO medium 610 and reflect at least aportion of the signal beam back into the OPO medium 610. By adding a HRor PR surface for the signal wavelength, a cross-resonant OPO may beconverted into a signal-resonant OPO with an external mirror M2. As anexample, surface S2 of mirror M2 may have a 50% reflectivity at thesignal wavelength, and approximately 50% of the signal light may be sentback to the OPO medium 610. The remaining 50% of the signal light may betransmitted through mirror M2 and directed to a splitter or scanner 120.

In particular embodiments, an OPO 600 may include an OPO medium 610 andone or more external mirrors. The external mirrors may have concavereflective surfaces that allow the spatial-mode size of the signal oridler to be controlled or optimized. For a flat-flat resonant-cavitydesign (e.g., as illustrated in FIGS. 13-14) with flat end mirrors(formed by surfaces 620 and 630), the spatial-mode control for thesignal and idler may be provided at least in part by parametric gainguiding from an OPO pump beam that has a relatively small diameter orhigh brightness. An OPO 600 that includes one or more external curvedmirrors may allow additional control over the spatial-mode size of thesignal beam. As an example, an OPO 600 may include an external concavemirror positioned facing back surface 620 (e.g., located between PQSWlaser 400 and back surface 620, with the concave surface facing backsurface 620) or facing output surface 630. As another example, an OPO600 may include two external mirrors, one mirror facing back surface 620and the other mirror facing output surface 630. A concave surface of amirror facing back surface 620 may have a coating that is AR for OPOpump light, HR for signal light, or AR, PR, or HR for idler light.Additionally, the back surface 620 may have a coating that is AR for OPOpump light, AR or HR for signal light, or AR, PR, or HR for idler light.A concave surface of a mirror facing output surface 630 may have acoating that is AR or PR for signal light or AR, PR, or HR for idlerlight. Additionally, the output surface 630 may have a coating that isHR for OPO pump light, AR or PR for signal light, or AR, PR, or HR foridler light.

FIG. 18 illustrates an example self-Raman laser 700 that includes a gainmedium 710 and a saturable absorber 420. In particular embodiments, aself-Raman laser 700 may refer to a solid-state laser that includes again medium 710, where, in addition to providing optical gain, the gainmedium 710 also includes a Raman-active material. A Raman-activematerial may refer to a host crystal that exhibits the Raman effect inwhich incident photons may be inelastically scattered by the hostcrystal to produce lower-energy scattered photons. An inelasticscattering process may cause an incident photon to be scattered andproduce a photon with a lower energy (or, longer wavelength), where theenergy difference between the incident and scattered photons is referredto as the Stokes shift. As an example, the YVO₄ host material of aNd:YVO₄ gain medium 710 may exhibit a Stokes shift of approximately 0.11eV (or, 894 cm⁻¹). For an incident photon with a wavelength ofapproximately 1342 nm (or, an energy of approximately 0.92 eV), a Stokesshift of 0.11 eV results in the production of a Raman-shifted photonwith a wavelength of approximately 1525 nm (or, an energy ofapproximately 0.81 eV).

In particular embodiments, a light source 110 of a lidar system 100 mayinclude a solid-state laser, where the solid-state laser includes aself-Raman laser 700 that includes a Raman-active gain medium 710 and aQ-switch (e.g., a saturable absorber 420 or an active Q-switch). Aself-Raman laser 700 may produce Q-switched pulses of light at a lasingwavelength of the self-Raman laser. A self-Raman laser 700 may operatein a manner similar to a Q-switched laser (e.g., gain medium 710 alongwith saturable absorber 420 or an active Q-switch may produce Q-switchedpulses through a Q-switching process). Additionally, the gain medium 710of a self-Raman laser 700 may include a Raman-active material (e.g., thehost crystal of gain medium 710 may be Raman active). At least a portionof the Q-switched pulses produced by the self-Raman laser 700 may beRaman-shifted in the Raman-active gain medium 710 to produceRaman-shifted pulses of light. The Raman-shifted pulses may have aRaman-shifted wavelength that is longer than the lasing wavelength, andthe self-Raman laser 700 may be configured to emit at least a portion ofthe Raman-shifted pulses. In particular embodiments, a passivelyQ-switched self-Raman laser (as illustrated in FIGS. 18 and 19) mayinclude a Raman-active gain medium 710 and a saturable absorber 420. Inparticular embodiments, an actively Q-switched self-Raman laser 700 mayinclude a Raman-active gain medium 710 and an active Q-switch, where thegain medium 710 and the active Q-switch are configured to produceoptical pulses through an active Q-switching process.

In particular embodiments, gain medium 710 of a self-Raman laser 700 mayinclude a host crystal doped with rare-earth ions, where the hostcrystal is a Raman-active material. In particular embodiments, aRaman-active host crystal of gain medium 710 may include diamond, anysuitable orthovanadate material, any suitable tungstate material, or anyother suitable material. As an example, the host crystal of gain medium710 may include yttrium orthovanadate (YVO₄), calcium tungstate (CaWO₄),potassium-gadolinium tungstate (KGd(WO₄)₂), barium tungstate (BaWO₄),strontium tungstate (SrWO₄), barium nitrate (Ba(NO₃)₂), or leadmolybdate (Nd:PbMoO₄). As another example, a Raman-active gain medium710 of a self-Raman laser 700 may include a rare-earth-dopedorthovanadate crystal or a rare-earth-doped tungstate crystal. Asanother example, a Raman-active gain medium 710 of a self-Raman laser700 may include neodymium-doped yttrium orthovanadate (Nd:YVO₄),neodymium-doped barium tungstate (Nd:BaWO₄), neodymium-doped strontiumtungstate (Nd:SrWO₄), or neodymium-doped lead molybdate (Nd:PbMoO₄).

In particular embodiments, a gain medium 710 of a self-Raman laser 700may have any suitable length L_(g) between approximately 1 mm andapproximately 30 mm. In particular embodiments, a self-Raman laser 700may include any suitable saturable absorber 420, such as for example,V:YAG, Cr:YAG, Co:spinel, or Nd:SrF₂. As an example, a self-Raman laser700 may include a 10-mm long Nd:YVO₄ gain medium 710 and a V:YAGsaturable absorber 420. As another example, a self-Raman laser 700 mayinclude a 10-mm long Nd:YVO₄ gain medium 710 with a 2-mm long end cap500.

In particular embodiments, a self-Raman laser 700, which may be referredto as a passively Q-switched (PQSW) self-Raman laser, may produce pulsesof light through a passive Q-switching process. Additionally, at least aportion of the Q-switched pulses of light may undergo a Raman-shiftingprocess which produces longer-wavelength pulses, and at least a portionof the longer-wavelength pulses may be emitted by the self-Raman laser700 as an output beam 460. As an example, a Nd:YVO₄ gain medium 710 andV:YAG saturable absorber 420 may act as a PQSW laser and produce opticalpulses at approximately 1342 nm. Additionally, the YVO₄ host crystal mayRaman shift at least some of the 1342-nm light to produce pulses oflight at approximately 1525 nm. The 1525-nm pulses of light may beemitted as output beam 460, and at least part of the output beam 460 mayform an output beam 125 of a lidar system 100. As another example, aself-Raman laser 700 may produce an output beam 460 with optical pulseshaving a pulse energy of greater than or equal to 1 μJ, a pulserepetition frequency of greater than or equal to 60 kHz, a pulseduration of less than or equal to 2 ns, or a wavelength of betweenapproximately 1400 nm and approximately 1600 nm.

In particular embodiments, a self-Raman laser 700 may operate in asimilar manner as a PQSW laser 400 described herein with the addition ofan intracavity Raman-shifting process that occurs within the hostcrystal of the gain medium 710. The Raman-shifting process may convertlaser photons (e.g., 1342-nm photons) produced by gain medium 710 intolonger-wavelength photons (e.g., 1525-nm photons). In particularembodiments, a self-Raman laser 700 may be configured to produce pulsesof output light 460 at a wavelength of approximately 1525 nm. As anexample, a self-Raman laser 700 may include a Nd:YVO₄ gain medium 710configured to lase (e.g., configured to produce laser light through astimulated-emission process) and produce optical pulses at a wavelengthof approximately 1342 nm. Additionally, the YVO₄ host material of thegain medium 710 may Raman shift at least a portion of the 1342-nm lightto produce the 1525-nm pulses of Raman-shifted light.

In particular embodiments, gain medium 710 of self-Raman laser 700 maybe pumped at a wavelength between approximately 800 nm and approximately1000 nm by an edge-emitter laser diode or a VECSEL. As an example, pumplaser 430 may be an edge-emitter laser diode with an output power ofgreater than or equal to 5 W and an operating wavelength betweenapproximately 805 nm and approximately 811 nm (e.g., approximately 808nm). Additionally, the free-space pump beam 440 may be focused by lens450 to have a 1/e² beam diameter of approximately 100-400 μm in gainmedium 710.

In the example of FIG. 18, gain medium 710 and saturable absorber 420are separated by an air gap 510 with a length L_(air). In particularembodiments, air gap 510 may have any suitable length L_(air) betweenapproximately 0 mm and approximately 50 mm. In particular embodiments,gain medium 710 and saturable absorber 420 may be separated by an airgap 510 to allow for differences in thermal expansion between the twohost crystals (e.g., YVO₄ and YAG may have different coefficients ofthermal expansion). As an example, gain medium 710 and saturableabsorber 420 may be separated by an air gap 510 with length L_(air) ofapproximately 0.05 mm, 0.1 mm, 0.5 mm, 1 mm, 2 mm, 5 mm, or 10 mm. Inparticular embodiments, there may be substantially no air gap 510between gain medium 710 and saturable absorber 420 so that L_(air) isapproximately zero (e.g., self-Raman laser 700 may not include surface Eor surface F). As an example, gain medium 710 and saturable absorber 420may be bonded together with adhesive, epoxy, optical contacting,diffusion bonding, chemically activated direct bonding, or any othersuitable bonding technique.

In particular embodiments, back surface 470 and output surface 480 of aself-Raman laser 700 may form two ends of a laser cavity of theself-Raman laser 700. As an example, a laser cavity of a self-Ramanlaser 700 may be resonant for a lasing wavelength of the gain medium 710(e.g., 1342 nm). Additionally, the laser cavity may be resonant for aRaman wavelength (e.g., 1525 nm). As an example, back surface 470 andoutput surface 480 may each have a coating that is HR for a lasingwavelength or HR or PR for a Raman wavelength. A Raman wavelength, whichmay be referred to as a Raman-shifted wavelength, may correspond to thewavelength of light produced in a self-Raman laser 700 through Ramanshifting.

In particular embodiments, back surface 470 of self-Raman laser 700 mayhave a dielectric coating which is AR (e.g., R<2%) at an operatingwavelength of pump laser 430, HR (e.g., R>98%) at a lasing wavelength ofthe self-Raman laser 700, or HR (e.g., R>98%) at a Raman wavelength. Asan example, back surface 470 may have a coating with the followingreflectivity values: R<1% at 805-811 nm; R>99.5% at approximately 1342nm; or R>99.5% at approximately 1525 nm. The pump-AR coating may allowmost of the pump beam 440 to enter the gain medium 710 with minimalreflection loss at back surface 470. The HR coating for the Ramanwavelength reflects most of the Raman-shifted light so that it isemitted primarily from the output surface 480.

In particular embodiments, output surface 480 of self-Raman laser 700may have a dielectric coating which is HR at an operating wavelength ofpump laser 430, HR at a lasing wavelength of the self-Raman laser 700,or AR or PR at a Raman wavelength. As an example, output surface 480 mayhave a coating with the following reflectivity values: R>99% at 805-811nm; R>99.5% at approximately 1342 nm; or R<1% or R≈=50% at approximately1525 nm. In particular embodiments, output surface 480 may have acoating with no particular reflectivity for the pump-laser wavelength(e.g., the pump beam 440 may be reflected by a pump-HR coating locatedat surface E or surface F). As an example, output surface 480 may have acoating with the following reflectivity values: R>99.5% at approximately1342 nm; or R<1% or 50% at approximately 1525 nm. Additionally, surfaceE or surface F may have an HR coating for the pump-laser wavelength. Apump-HR coating on surface E, surface F, or output surface 480 may allowthe pump beam 440 to make two passes through the gain medium 710.

In particular embodiments, if self-Raman laser 700 includes an air gap510 with a nonzero thickness (e.g., L_(air)>0), then surface E andsurface F may each have a dielectric coating with particularreflectivity at particular wavelengths. As an example, surface E mayhave a coating which is HR at a pump-laser wavelength, AR at a laserwavelength of the self-Raman laser 700, or AR at a Raman wavelength. Forexample, surface E may have a coating with the following reflectivityvalues: R>99% at 805-811 nm; R<1% at approximately 1342 nm; or R<1% atapproximately 1525 nm. As another example, surface F may have a coatingwhich is AR at a laser wavelength of the self-Raman laser 700 or AR at aRaman wavelength. For example, surface F may have a coating with thefollowing reflectivity values: R<1% at approximately 1342 nm; or R<1% atapproximately 1525 nm. If surface E includes a pump-HR coating, thensurface F may have a coating with no particular reflectivity at apump-laser wavelength, since most of the pump beam 440 may be reflectedby surface E.

FIG. 19 illustrates an example self-Raman laser 700 that includes alaser-cavity mirror 720 and an end cap 500. In particular embodiments,self-Raman laser 700 may include an end cap 500 coupled to gain medium710, where the end cap 500 has a length L_(ec) and is substantially freeof gain-material dopants or has a low concentration of gain-materialdopants. As an example, an end cap 500 may include a separate piece ofundoped material (e.g., YVO₄) that is bonded to gain medium 710 (e.g.,Nd:YVO₄). As another example, an end cap 500 may be formed from anundoped portion of a host crystal of gain medium 710. For example, asingle YVO₄ host crystal with an overall length L_(ec)+L_(g) may bedoped with Nd ions over a length L_(g), and the remaining L_(ec) portionmay be an undoped end cap 500 that is substantially free of Nd dopants.In particular embodiments, end cap 500 may be positioned to receive pumpbeam 440 so that pump beam 440 propagates through the end cap 500 beforeentering gain medium 710. In particular embodiments, end cap 500 may actas a heat spreader that reduces thermally induced stress or thermallyinduced lensing within gain medium 410. In particular embodiments, aself-Raman laser 700 may include an end cap 500 and may not include anexternal laser-cavity mirror 720. As an example, surface D of end cap500 in FIG. 19 may act as a back surface 470 of self-Raman laser 700 andmay have a similar dielectric coating as back surface 470 describedabove with respect to FIG. 18.

In particular embodiments, self-Raman laser 700 may have any suitableoverall cavity length, where the cavity length corresponds to a distancebetween back surface 470 and output surface 480. As an example, aself-Raman laser 700 may have a cavity length of approximately 5 mm, 10mm, 15 mm, 20 mm, 25 mm, 50 mm, or any other suitable cavity-lengthvalue. As another example, a self-Raman laser 700 may have a gain-mediumlength L_(g) of approximately 10 mm and an overall cavity length ofapproximately 10.1-20 mm. As another example, a self-Raman laser 700 mayhave a gain-medium length L_(g) of approximately 10 mm, an end-caplength L_(ec) of approximately 2 mm, and an overall cavity length ofapproximately 20 mm. In the example of FIG. 18, the cavity length isL_(g)+L_(air)+L_(sa). In the example of FIG. 19, the cavity length isL_(air-1)+L_(ec)+L_(g)+L_(air-2)+L_(sa).

In particular embodiments, a self-Raman laser 700 may include one ormore air gaps. In the example of FIG. 19, self-Raman laser 700 includestwo air gaps: air gap 510-1 with length L_(air-1) and air gap 510-2 withlength L_(air-2). Air gap 510-2 in FIG. 19 may be similar to air gap 510in FIG. 18. As an example, the self-Raman laser 700 in FIG. 19 mayinclude an air gap 510-2 having any suitable length L_(air-2) betweenapproximately 0 mm and approximately 50 mm. If there is substantially noair gap 510-2 between gain medium 710 and saturable absorber 420 (e.g.,L_(air-2)=0), then saturable absorber 420 may be bonded to gain medium710, and self-Raman laser 700 may not include surface E or surface F.

In particular embodiments, a self-Raman laser 700 may includelaser-cavity mirror 720 separated from gain medium 710 by air gap 510-1.As an example, mirror 720 may include a back surface 470 that is concaveor convex and that forms a cavity mirror of the self-Raman laser 700.The distance L_(air-1) between back surface 470 and surface D may be anysuitable value between approximately 0 mm and approximately 50 mm. As anexample, L_(air-1) may be approximately 0.5 mm, 1 mm, 2 mm, 3 mm, 5 mm,10 mm, or 20 mm. In particular embodiments, back surface 470 of mirror720 may have any suitable radius of curvature, such as for example, aradius of curvature of approximately +200 mm, +150 mm, +100 mm, +50 mm,+25 mm, −25 mm, −50 mm, −75 mm, −100 mm, −150 mm, or −200 mm.

In particular embodiments, surface C and back surface 470 of mirror 720may each have any suitable dielectric coating. As an example, surface Cmay have a coating which is AR at a pump-laser wavelength (e.g., R<0.5%at 805-811 nm) so that pump beam 440 passes through surface C withminimal reflection loss. As another example, back surface 470 of mirror720 have a coating which is AR at a pump-laser wavelength, HR at alasing wavelength of the self-Raman laser 700, or HR at a Ramanwavelength. For example, back surface 470 may have a coating with thefollowing reflectivity values: R<1% at 805-811 nm; R>99.8% atapproximately 1342 nm; or R>99.8% at approximately 1525 nm. As anotherexample, back surface 470 may have no particular reflectivity at a Ramanwavelength (e.g., surface D may have an HR coating that reflects theRaman wavelength).

In particular embodiments, surface D may be part of end cap 500 (asillustrated in FIG. 19), or surface D may be part of gain medium 710(e.g., if self-Raman laser 700 does not include an end cap 500). Inparticular embodiments, surface D may have a dielectric coating which isAR at a pump-laser wavelength, AR at a lasing wavelength of theself-Raman laser 700, or AR, PR, or HR at a Raman wavelength. Thepump-AR coating may allow most of the pump beam 440 to enter the end cap500 or gain medium 710 with minimal reflection loss at surface D. The ARcoating at the lasing wavelength may allow the laser light (e.g., lightat 1342 nm) to propagate to and from the cavity mirror 720 with minimalloss at surface D. If back surface 470 has an HR coating at a Ramanwavelength, then surface D may have an AR coating at the Ramanwavelength. Alternately, if back surface 470 has no particularreflectivity at a Raman wavelength, then surface D may have an HRcoating at the Raman wavelength.

FIG. 20 illustrates an example computer system 800. In particularembodiments, one or more computer systems 800 may perform one or moresteps of one or more methods described or illustrated herein. Inparticular embodiments, one or more computer systems 800 may providefunctionality described or illustrated herein. In particularembodiments, software running on one or more computer systems 800 mayperform one or more steps of one or more methods described orillustrated herein or may provide functionality described or illustratedherein. Particular embodiments may include one or more portions of oneor more computer systems 800. In particular embodiments, a computersystem may be referred to as a computing device, a computing system, acomputer, a general-purpose computer, or a data-processing apparatus.Herein, reference to a computer system may encompass one or morecomputer systems, where appropriate.

Computer system 800 may take any suitable physical form. As an example,computer system 800 may be an embedded computer system, a system-on-chip(SOC), a single-board computer system (SBC), a desktop computer system,a laptop or notebook computer system, a mainframe, a mesh of computersystems, a server, a tablet computer system, or any suitable combinationof two or more of these. As another example, all or part of computersystem 800 may be combined with, coupled to, or integrated into avariety of devices, including, but not limited to, a camera, camcorder,personal digital assistant (PDA), mobile telephone, smartphone,electronic reading device (e.g., an e-reader), game console, smartwatch, clock, calculator, television monitor, flat-panel display,computer monitor, vehicle display (e.g., odometer display or dashboarddisplay), vehicle navigation system, lidar system, ADAS, autonomousvehicle, autonomous-vehicle driving system, cockpit control, camera viewdisplay (e.g., display of a rear-view camera in a vehicle), eyewear, orhead-mounted display. Where appropriate, computer system 800 may includeone or more computer systems 800; be unitary or distributed; spanmultiple locations; span multiple machines; span multiple data centers;or reside in a cloud, which may include one or more cloud components inone or more networks. Where appropriate, one or more computer systems800 may perform without substantial spatial or temporal limitation oneor more steps of one or more methods described or illustrated herein. Asan example, one or more computer systems 800 may perform in real time orin batch mode one or more steps of one or more methods described orillustrated herein. One or more computer systems 800 may perform atdifferent times or at different locations one or more steps of one ormore methods described or illustrated herein, where appropriate.

As illustrated in the example of FIG. 20, computer system 800 mayinclude a processor 810, memory 820, storage 830, an input/output (I/O)interface 840, a communication interface 850, or a bus 860. Computersystem 800 may include any suitable number of any suitable components inany suitable arrangement.

In particular embodiments, processor 810 may include hardware forexecuting instructions, such as those making up a computer program. Asan example, to execute instructions, processor 810 may retrieve (orfetch) the instructions from an internal register, an internal cache,memory 820, or storage 830; decode and execute them; and then write oneor more results to an internal register, an internal cache, memory 820,or storage 830. In particular embodiments, processor 810 may include oneor more internal caches for data, instructions, or addresses. Processor810 may include any suitable number of any suitable internal caches,where appropriate. As an example, processor 810 may include one or moreinstruction caches, one or more data caches, or one or more translationlookaside buffers (TLBs). Instructions in the instruction caches may becopies of instructions in memory 820 or storage 830, and the instructioncaches may speed up retrieval of those instructions by processor 810.Data in the data caches may be copies of data in memory 820 or storage830 for instructions executing at processor 810 to operate on; theresults of previous instructions executed at processor 810 for access bysubsequent instructions executing at processor 810 or for writing tomemory 820 or storage 830; or other suitable data. The data caches mayspeed up read or write operations by processor 810. The TLBs may speedup virtual-address translation for processor 810. In particularembodiments, processor 810 may include one or more internal registersfor data, instructions, or addresses. Processor 810 may include anysuitable number of any suitable internal registers, where appropriate.Where appropriate, processor 810 may include one or more arithmeticlogic units (ALUs); may be a multi-core processor; or may include one ormore processors 810.

In particular embodiments, memory 820 may include main memory forstoring instructions for processor 810 to execute or data for processor810 to operate on. As an example, computer system 800 may loadinstructions from storage 830 or another source (such as, for example,another computer system 800) to memory 820. Processor 810 may then loadthe instructions from memory 820 to an internal register or internalcache. To execute the instructions, processor 810 may retrieve theinstructions from the internal register or internal cache and decodethem. During or after execution of the instructions, processor 810 maywrite one or more results (which may be intermediate or final results)to the internal register or internal cache. Processor 810 may then writeone or more of those results to memory 820. One or more memory buses(which may each include an address bus and a data bus) may coupleprocessor 810 to memory 820. Bus 860 may include one or more memorybuses. In particular embodiments, one or more memory management units(MMUs) may reside between processor 810 and memory 820 and facilitateaccesses to memory 820 requested by processor 810. In particularembodiments, memory 820 may include random access memory (RAM). This RAMmay be volatile memory, where appropriate. Where appropriate, this RAMmay be dynamic RAM (DRAM) or static RAM (SRAM). Memory 820 may includeone or more memories 820, where appropriate.

In particular embodiments, storage 830 may include mass storage for dataor instructions. As an example, storage 830 may include a hard diskdrive (HDD), a floppy disk drive, flash memory, an optical disc, amagneto-optical disc, magnetic tape, or a Universal Serial Bus (USB)drive or a combination of two or more of these. Storage 830 may includeremovable or non-removable (or fixed) media, where appropriate. Storage830 may be internal or external to computer system 800, whereappropriate. In particular embodiments, storage 830 may be non-volatile,solid-state memory. In particular embodiments, storage 830 may includeread-only memory (ROM). Where appropriate, this ROM may be mask ROM(MROM), programmable ROM (PROM), erasable PROM (EPROM), electricallyerasable PROM (EEPROM), flash memory, or a combination of two or more ofthese. Storage 830 may include one or more storage control unitsfacilitating communication between processor 810 and storage 830, whereappropriate. Where appropriate, storage 830 may include one or morestorages 830.

In particular embodiments, I/O interface 840 may include hardware,software, or both, providing one or more interfaces for communicationbetween computer system 800 and one or more I/O devices. Computer system800 may include one or more of these I/O devices, where appropriate. Oneor more of these I/O devices may enable communication between a personand computer system 800. As an example, an I/O device may include akeyboard, keypad, microphone, monitor, mouse, printer, scanner, speaker,camera, stylus, tablet, touch screen, trackball, another suitable I/Odevice, or any suitable combination of two or more of these. An I/Odevice may include one or more sensors. Where appropriate, I/O interface840 may include one or more device or software drivers enablingprocessor 810 to drive one or more of these I/O devices. I/O interface840 may include one or more I/O interfaces 840, where appropriate.

In particular embodiments, communication interface 850 may includehardware, software, or both providing one or more interfaces forcommunication (such as, for example, packet-based communication) betweencomputer system 800 and one or more other computer systems 800 or one ormore networks. As an example, communication interface 850 may include anetwork interface controller (NIC) or network adapter for communicatingwith an Ethernet or other wire-based network or a wireless NIC (WNIC); awireless adapter for communicating with a wireless network, such as aWI-FI network; or an optical transmitter (e.g., a laser or alight-emitting diode) or an optical receiver (e.g., a photodetector) forcommunicating using fiber-optic communication or free-space opticalcommunication. Computer system 800 may communicate with an ad hocnetwork, a personal area network (PAN), an in-vehicle network (IVN), alocal area network (LAN), a wide area network (WAN), a metropolitan areanetwork (MAN), or one or more portions of the Internet or a combinationof two or more of these. One or more portions of one or more of thesenetworks may be wired or wireless. As an example, computer system 800may communicate with a wireless PAN (WPAN) (such as, for example, aBLUETOOTH WPAN), a WI-FI network, a Worldwide Interoperability forMicrowave Access (WiMAX) network, a cellular telephone network (such as,for example, a Global System for Mobile Communications (GSM) network),or other suitable wireless network or a combination of two or more ofthese. As another example, computer system 800 may communicate usingfiber-optic communication based on 100 Gigabit Ethernet (100 GbE), 10Gigabit Ethernet (10 GbE), or Synchronous Optical Networking (SONET).Computer system 800 may include any suitable communication interface 850for any of these networks, where appropriate. Communication interface850 may include one or more communication interfaces 850, whereappropriate.

In particular embodiments, bus 860 may include hardware, software, orboth coupling components of computer system 800 to each other. As anexample, bus 860 may include an Accelerated Graphics Port (AGP) or othergraphics bus, a controller area network (CAN) bus, an Enhanced IndustryStandard Architecture (EISA) bus, a front-side bus (FSB), aHYPERTRANSPORT (HT) interconnect, an Industry Standard Architecture(ISA) bus, an INFINIBAND interconnect, a low-pin-count (LPC) bus, amemory bus, a Micro Channel Architecture (MCA) bus, a PeripheralComponent Interconnect (PCI) bus, a PCI-Express (PCIe) bus, a serialadvanced technology attachment (SATA) bus, a Video Electronics StandardsAssociation local bus (VLB), or another suitable bus or a combination oftwo or more of these. Bus 860 may include one or more buses 860, whereappropriate.

Various example embodiments are described in the following paragraphs.

In some embodiments, a lidar system comprises: a Q-switched laserconfigured to emit pulses of light, wherein the Q-switched lasercomprises a gain medium and a Q-switch; a scanner configured to scan theemitted pulses of light across a field of regard; a receiver configuredto detect at least a portion of the scanned pulses of light scattered bya target located a distance from the lidar system; and a processorconfigured to determine the distance from the lidar system to the targetbased at least in part on a round-trip time of flight for an emittedpulse of light to travel from the lidar system to the target and back tothe lidar system.

In some embodiments, the Q-switched laser is an actively Q-switchedlaser and the Q-switch is an active Q-switch.

In some embodiments, the Q-switched laser is a passively Q-switched(PQSW) laser and the Q-switch is a saturable absorber.

In some embodiments, the saturable absorber comprises vanadium-dopedyttrium aluminum garnet (V:YAG), chromium-doped YAG (Cr:YAG),cobalt-doped MgAl₂O₄ (Co:spinel), neodymium-doped strontium fluoride(Nd:SrF₂), or lithium fluoride with F₂ ⁻ color centers (LiF:F₂).

In some embodiments, the gain medium and the saturable absorber areseparated by an air gap.

In some embodiments, the saturable absorber is bonded to the gainmedium.

In some embodiments, the gain medium comprises neodymium-doped yttriumaluminum garnet (Nd:YAG), ytterbium-doped yttrium aluminum garnet(Yb:YAG), neodymium-doped yttrium orthovanadate (Nd:YVO₄),neodymium-doped yttrium scandium gallium garnet (Nd:YSGG),neodymium-doped gadolinium scandium gallium garnet (Nd:GSGG),neodymium-doped yttrium aluminum perovskite (Nd:YAP), or neodymium-dopedyttrium lithium fluoride (Nd:YLF).

In some embodiments, the gain medium comprises a back surface with adielectric coating having a low reflectivity at a pump-laser wavelengthand a high reflectivity at an operating wavelength of the Q-switchedlaser.

In some embodiments, the gain medium is pumped at a pump wavelengthbetween approximately 800 nm and approximately 1000 nm by anedge-emitter laser diode or a vertical-external-cavity surface-emittinglaser.

In some embodiments, the Q-switched laser is an eye-safe laser with anoperating wavelength between approximately 1400 nm and approximately1600 nm.

In some embodiments, an operating wavelength of the Q-switched laser isapproximately 1030 nanometers, approximately 1064 nanometers, or betweenapproximately 1400 nanometers and approximately 1480 nanometers.

In some embodiments, the Q-switched laser further comprises an end capcoupled to the gain medium, wherein: the end cap is substantially freeof gain-material dopants; and the end cap is positioned to receive lightfrom a pump laser so that the pump-laser light propagates through theend cap before entering the gain medium.

In some embodiments, the pulses of light emitted by the Q-switched laserhave a pulse repetition frequency greater than or equal to 20 kHz.

In some embodiments, the pulses of light emitted by the Q-switched laserhave optical characteristics comprising: a pulse duration less than orequal to 20 nanoseconds; a duty cycle less than or equal to 1%; a pulseenergy greater than or equal to 10 nanojoules; and a peak power greaterthan or equal to 1 watt.

In some embodiments, the lidar system further comprises a splitterconfigured to receive the pulses of light emitted by the Q-switchedlaser and split each received pulse of light into two or more angularlyseparated pulses of light which are scanned by the scanner across thefield of regard.

In some embodiments, the angularly separated pulses of light are scannedalong a scanning direction; and the angularly separated pulses of lightare split along a direction that is approximately orthogonal to thescanning direction.

In some embodiments, the receiver comprises an array of two or moredetector elements, wherein each detector element is configured to detectscattered light from a respective pulse of the two or more angularlyseparated pulses of light which are scanned across the field of regard.

In some embodiments, the field of regard comprises: a horizontal fieldof regard greater than or equal to 25 degrees; and a vertical field ofregard greater than or equal to 5 degrees.

In some embodiments, the scanner comprises one or more mirrors, whereineach mirror is mechanically driven by a galvanometer scanner, a resonantscanner, a microelectromechanical systems (MEMS) device, or a voice coilmotor.

In some embodiments, an output beam of the lidar system comprises theemitted pulses of light which are scanned across the field of regard; aninput beam of the lidar system comprises the portion of the scannedpulses of light detected by the receiver; and the input and output beamsare substantially coaxial.

In some embodiments, the lidar system further comprises an overlapmirror configured to overlap the input and output beams so that they aresubstantially coaxial, wherein the overlap mirror comprises: a hole,slot, or aperture which the output beam passes through; and a reflectingsurface that reflects at least a portion of the input beam toward thereceiver.

In some embodiments, scanning the emitted pulses of light across thefield of regard comprises scanning a field of view of the Q-switchedlaser across the field of regard; and the scanner is further configuredto scan a field of view of the receiver across the field of regard,wherein the Q-switched-laser field of view and the receiver field ofview are scanned synchronously with respect to one another.

In some embodiments, a lidar system comprises: a pump laser configuredto produce pulses of light at a pump wavelength; an optical parametricoscillator (OPO) comprising an OPO medium configured to: receive thepump pulses from the pump laser; convert at least part of the receivedpump pulses into pulses of light at a signal wavelength and pulses oflight at an idler wavelength; and emit at least a portion of the signalpulses; a scanner configured to scan the emitted pulses of light acrossa field of regard; a receiver configured to detect at least a portion ofthe scanned pulses of light scattered by a target located a distancefrom the lidar system; and a processor configured to determine thedistance from the lidar system to the target based at least in part on around-trip time of flight for an emitted pulse of light to travel fromthe lidar system to the target and back to the lidar system.

In some embodiments, the pump laser is an actively Q-switched lasercomprising a gain medium and an active Q-switch.

In some embodiments, the pump laser is a passively Q-switched (PQSW)laser comprising a gain medium and a saturable absorber.

In some embodiments, the gain medium is pumped by an edge-emitter laserdiode or a vertical-external-cavity surface-emitting laser with anoperating wavelength between approximately 800 nm and approximately 1000nm.

In some embodiments, the gain medium comprises neodymium-doped yttriumaluminum garnet (Nd:YAG), ytterbium-doped yttrium aluminum garnet(Yb:YAG), neodymium-doped yttrium orthovanadate (Nd:YVO₄),neodymium-doped yttrium scandium gallium garnet (Nd:YSGG),neodymium-doped gadolinium scandium gallium garnet (Nd:GSGG),neodymium-doped yttrium aluminum perovskite (Nd:YAP), or neodymium-dopedyttrium lithium fluoride (Nd:YLF); and the saturable absorber comprisesvanadium-doped yttrium aluminum garnet (V:YAG), chromium-doped YAG(Cr:YAG), cobalt-doped MgAl₂O₄ (Co:spinel), neodymium-doped strontiumfluoride (Nd:SrF₂), or lithium fluoride with F₂ ⁻ color centers(LiF:F₂).

In some embodiments, the pump wavelength is approximately 1030 nm orapproximately 1064 nm.

In some embodiments, the pump wavelength (λ_(p)), signal wavelength(λ_(s)), and idler wavelength (λ_(i)) are at least approximately relatedby an expression 1/λ_(p)=1/λ_(s)+1/λ_(i), wherein: λ_(i), is less thanλ_(s) and j; and λ_(s) is less than λ_(i).

In some embodiments, the OPO is an eye-safe light source and the signalwavelength of the signal pulses emitted by the OPO is betweenapproximately 1400 nm and approximately 1600 nm.

In some embodiments, the OPO medium comprises periodically poledpotassium titanyl phosphate (PPKTP), periodically poled potassiumtitanyl arsenate (PPKTA), periodically poled rubidium titanyl arsenate(PPRTA), periodically poled lithium niobate (PPLN), periodically poledlithium tantalate (PPLT), or periodically poled stoichiometric lithiumtantalate (PPSLT).

In some embodiments, the OPO medium comprises a back surface and anoutput surface, wherein: the back surface comprises a dielectric coatingwith low reflectivity for the pump wavelength and high reflectivity forthe signal wavelength; and the output surface comprises a dielectriccoating with high reflectivity for the pump wavelength and low orpartial reflectivity for the signal wavelength.

In some embodiments, the coating of the back surface additionally hashigh reflectivity or low reflectivity for the idler wavelength; and thecoating of the output surface additionally has high reflectivity or lowreflectivity for the idler wavelength.

In some embodiments, the signal pulses of light emitted by the OPO havea pulse repetition frequency greater than or equal to 20 kHz.

In some embodiments, the signal pulses of light emitted by the OPO haveoptical characteristics comprising: a pulse duration less than or equalto 20 nanoseconds; a duty cycle less than or equal to 1%; a pulse energygreater than or equal to 10 nanojoules; and a peak power greater than orequal to 1 watt.

In some embodiments, the lidar system further comprises a splitterconfigured to receive the signal pulses of light emitted by the OPO andsplit each received pulse of light into two or more angularly separatedpulses of light which are scanned by the scanner across the field ofregard.

In some embodiments, the angularly separated pulses of light are scannedalong a scanning direction; and the angularly separated pulses of lightare split along a direction that is approximately orthogonal to thescanning direction.

In some embodiments, the receiver comprises an array of two or moredetector elements, wherein each detector element is configured to detectscattered light from a respective pulse of the two or more angularlyseparated pulses of light which are scanned across the field of regard.

In some embodiments, the field of regard comprises: a horizontal fieldof regard greater than or equal to 25 degrees; and a vertical field ofregard greater than or equal to 5 degrees.

In some embodiments, the scanner comprises one or more mirrors, whereineach mirror is mechanically driven by a galvanometer scanner, a resonantscanner, a microelectromechanical systems (MEMS) device, or a voice coilmotor.

In some embodiments, an output beam of the lidar system comprises theemitted signal pulses of light which are scanned across the field ofregard; an input beam of the lidar system comprises the portion of thescanned pulses of light detected by the receiver; and the input andoutput beams are substantially coaxial.

In some embodiments, the lidar system further comprises an overlapmirror configured to overlap the input and output beams so that they aresubstantially coaxial, wherein the overlap mirror comprises: a hole,slot, or aperture which the output beam passes through; and a reflectingsurface that reflects at least a portion of the input beam toward thereceiver.

In some embodiments, scanning the emitted pulses of light across thefield of regard comprises scanning a field of view of the OPO across thefield of regard; and the scanner is further configured to scan a fieldof view of the receiver across the field of regard, wherein the OPOfield of view and the receiver field of view are scanned synchronouslywith respect to one another.

In some embodiments, a lidar system comprises: a self-Raman lasercomprising a Raman-active gain medium and a Q-switch, wherein theself-Raman laser is configured to: produce Q-switched pulses of light ata lasing wavelength of the self-Raman laser; Raman-shift, in theRaman-active gain medium, at least a portion of the Q-switched pulses toproduce Raman-shifted pulses of light, wherein the Raman-shifted pulseshave a Raman-shifted wavelength that is longer than the lasingwavelength; and emit at least a portion of the Raman-shifted pulses; ascanner configured to scan the emitted pulses of light across a field ofregard; a receiver configured to detect at least a portion of thescanned pulses of light scattered by a target located a distance fromthe lidar system; and a processor configured to determine the distancefrom the lidar system to the target based at least in part on around-trip time of flight for an emitted pulse of light to travel fromthe lidar system to the target and back to the lidar system.

In some embodiments, the self-Raman laser is an actively Q-switchedself-Raman laser and the Q-switch is an active Q-switch.

In some embodiments, the self-Raman laser is a passively Q-switched(PQSW) self-Raman laser and the Q-switch is a saturable absorber.

In some embodiments, the saturable absorber comprises vanadium-dopedyttrium aluminum garnet (V:YAG), cobalt-doped MgAl₂O₄ (Co:spinel), orneodymium-doped strontium fluoride (Nd:SrF₂).

In some embodiments, the Raman-active gain medium comprises arare-earth-doped orthovanadate crystal or a rare-earth-doped tungstatecrystal.

In some embodiments, the Raman-active gain medium comprisesneodymium-doped yttrium orthovanadate (Nd:YVO₄) comprising neodymiumions in a yttrium orthovanadate (YVO₄) host crystal, wherein: the lasingwavelength of the Q-switched pulses of light produced by the Nd:YVO₄material is approximately 1342 nm; and the YVO₄ host crystal isconfigured to Raman shift the portion of the Q-switched pulses toproduce the Raman-shifted pulses of light, wherein the Raman-shiftedwavelength is approximately 1525 nm.

In some embodiments, the gain medium is pumped at a wavelength betweenapproximately 800 nm and approximately 1000 nm by an edge-emitter laserdiode or a vertical-external-cavity surface-emitting laser.

In some embodiments, the self-Raman laser further comprises an end capcoupled to the gain medium, wherein: the end cap is substantially freeof gain-material dopants; and the end cap is positioned to receive lightfrom a pump laser so that the pump-laser light propagates through theend cap before entering the gain medium.

In some embodiments, the self-Raman laser further comprises a backsurface with a dielectric coating having low reflectivity at apump-laser wavelength, high reflectivity at the lasing wavelength of theself-Raman laser, and high reflectivity at the Raman-shifted wavelength.

In some embodiments, the self-Raman laser further comprises an outputsurface with a dielectric coating having high reflectivity at the lasingwavelength of the self-Raman laser and high reflectivity, partialreflectivity, or low reflectivity at the Raman-shifted wavelength.

In some embodiments, the self-Raman laser further comprises a mirrorseparated from the gain medium by an air gap, wherein the mirrorcomprises a concave surface that forms a cavity mirror of the self-Ramanlaser, wherein the concave surface comprises a back surface with adielectric coating having low reflectivity at a pump-laser wavelength,high reflectivity at the lasing wavelength of the self-Raman laser, andhigh reflectivity at the Raman-shifted wavelength.

In some embodiments, the self-Raman laser is an eye-safe laser with anoperating wavelength between approximately 1400 nm and approximately1600 nm.

In some embodiments, the pulses of light emitted by the self-Raman laserhave a pulse repetition frequency greater than or equal to 20 kHz.

In some embodiments, the pulses of light emitted by the self-Raman laserhave optical characteristics comprising: a pulse duration less than orequal to 20 nanoseconds; a duty cycle less than or equal to 1%; a pulseenergy greater than or equal to 10 nanojoules; and a peak power greaterthan or equal to 1 watt.

In some embodiments, the lidar system further comprises a splitterconfigured to receive the pulses of light emitted by the self-Ramanlaser and split each received pulse of light into two or more angularlyseparated pulses of light which are scanned by the scanner across thefield of regard.

In some embodiments, the angularly separated pulses of light are scannedalong a scanning direction; and the angularly separated pulses of lightare split along a direction that is approximately orthogonal to thescanning direction.

In some embodiments, the receiver comprises an array of two or moredetector elements, wherein each detector element is configured to detectscattered light from a respective pulse of the two or more angularlyseparated pulses of light which are scanned across the field of regard.

In some embodiments, the field of regard comprises: a horizontal fieldof regard greater than or equal to 25 degrees; and a vertical field ofregard greater than or equal to 5 degrees.

In some embodiments, the scanner comprises one or more mirrors, whereineach mirror is mechanically driven by a galvanometer scanner, a resonantscanner, a microelectromechanical systems (MEMS) device, or a voice coilmotor.

In some embodiments, an output beam of the lidar system comprises theemitted pulses of light which are scanned across the field of regard; aninput beam of the lidar system comprises the portion of the scannedpulses of light detected by the receiver; and the input and output beamsare substantially coaxial.

In some embodiments, the lidar system further comprises an overlapmirror configured to overlap the input and output beams so that they aresubstantially coaxial, wherein the overlap mirror comprises: a hole,slot, or aperture which the output beam passes through; and a reflectingsurface that reflects at least a portion of the input beam toward thereceiver.

In some embodiments, scanning the emitted pulses of light across thefield of regard comprises scanning a field of view of the self-Ramanlaser across the field of regard; and the scanner is further configuredto scan a field of view of the receiver across the field of regard,wherein the self-Raman-laser field of view and the receiver field ofview are scanned synchronously with respect to one another.

In particular embodiments, various modules, circuits, systems, methods,or algorithm steps described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or any suitable combination of hardware and software. Inparticular embodiments, computer software (which may be referred to assoftware, computer-executable code, computer code, a computer program,computer instructions, or instructions) may be used to perform variousfunctions described or illustrated herein, and computer software may beconfigured to be executed by or to control the operation of computersystem 800. As an example, computer software may include instructionsconfigured to be executed by processor 810. In particular embodiments,owing to the interchangeability of hardware and software, the variousillustrative logical blocks, modules, circuits, or algorithm steps havebeen described generally in terms of functionality. Whether suchfunctionality is implemented in hardware, software, or a combination ofhardware and software may depend upon the particular application ordesign constraints imposed on the overall system.

In particular embodiments, a computing device may be used to implementvarious modules, circuits, systems, methods, or algorithm stepsdisclosed herein. As an example, all or part of a module, circuit,system, method, or algorithm disclosed herein may be implemented orperformed by a general-purpose single- or multi-chip processor, adigital signal processor (DSP), an ASIC, a FPGA, any other suitableprogrammable-logic device, discrete gate or transistor logic, discretehardware components, or any suitable combination thereof. Ageneral-purpose processor may be a microprocessor, or, any conventionalprocessor, controller, microcontroller, or state machine. A processormay also be implemented as a combination of computing devices, e.g., acombination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

In particular embodiments, one or more implementations of the subjectmatter described herein may be implemented as one or more computerprograms (e.g., one or more modules of computer-program instructionsencoded or stored on a computer-readable non-transitory storage medium).As an example, the steps of a method or algorithm disclosed herein maybe implemented in a processor-executable software module which mayreside on a computer-readable non-transitory storage medium. Inparticular embodiments, a computer-readable non-transitory storagemedium may include any suitable storage medium that may be used to storeor transfer computer software and that may be accessed by a computersystem. Herein, a computer-readable non-transitory storage medium ormedia may include one or more semiconductor-based or other integratedcircuits (ICs) (such, as for example, field-programmable gate arrays(FPGAs) or application-specific ICs (ASICs)), hard disk drives (HDDs),hybrid hard drives (HHDs), optical discs (e.g., compact discs (CDs),CD-ROM, digital versatile discs (DVDs), blue-ray discs, or laser discs),optical disc drives (ODDs), magneto-optical discs, magneto-opticaldrives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes,flash memories, solid-state drives (SSDs), RAM, RAM-drives, ROM, SECUREDIGITAL cards or drives, any other suitable computer-readablenon-transitory storage media, or any suitable combination of two or moreof these, where appropriate. A computer-readable non-transitory storagemedium may be volatile, non-volatile, or a combination of volatile andnon-volatile, where appropriate.

In particular embodiments, certain features described herein in thecontext of separate implementations may also be combined and implementedin a single implementation. Conversely, various features that aredescribed in the context of a single implementation may also beimplemented in multiple implementations separately or in any suitablesub-combination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination may in some cases be excisedfrom the combination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

While operations may be depicted in the drawings as occurring in aparticular order, this should not be understood as requiring that suchoperations be performed in the particular order shown or in sequentialorder, or that all operations be performed. Further, the drawings mayschematically depict one more example processes or methods in the formof a flow diagram or a sequence diagram. However, other operations thatare not depicted may be incorporated in the example processes or methodsthat are schematically illustrated. For example, one or more additionaloperations may be performed before, after, simultaneously with, orbetween any of the illustrated operations. Moreover, one or moreoperations depicted in a diagram may be repeated, where appropriate.Additionally, operations depicted in a diagram may be performed in anysuitable order. Furthermore, although particular components, devices, orsystems are described herein as carrying out particular operations, anysuitable combination of any suitable components, devices, or systems maybe used to carry out any suitable operation or combination ofoperations. In certain circumstances, multitasking or parallelprocessing operations may be performed. Moreover, the separation ofvarious system components in the implementations described herein shouldnot be understood as requiring such separation in all implementations,and it should be understood that the described program components andsystems may be integrated together in a single software product orpackaged into multiple software products.

Various embodiments have been described in connection with theaccompanying drawings. However, it should be understood that the figuresmay not necessarily be drawn to scale. As an example, distances orangles depicted in the figures are illustrative and may not necessarilybear an exact relationship to actual dimensions or layout of the devicesillustrated.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes or illustrates respective embodimentsherein as including particular components, elements, functions,operations, or steps, any of these embodiments may include anycombination or permutation of any of the components, elements,functions, operations, or steps described or illustrated anywhere hereinthat a person having ordinary skill in the art would comprehend.

The term “or” as used herein is to be interpreted as an inclusive ormeaning any one or any combination, unless expressly indicated otherwiseor indicated otherwise by context. Therefore, herein, the expression “Aor B” means “A, B, or both A and B.” As another example, herein, “A, Bor C” means at least one of the following: A; B; C; A and B; A and C; Band C; A, B and C. An exception to this definition will occur if acombination of elements, devices, steps, or operations is in some wayinherently mutually exclusive.

As used herein, words of approximation such as, without limitation,“approximately, “substantially,” or “about” refer to a condition thatwhen so modified is understood to not necessarily be absolute or perfectbut would be considered close enough to those of ordinary skill in theart to warrant designating the condition as being present. The extent towhich the description may vary will depend on how great a change can beinstituted and still have one of ordinary skill in the art recognize themodified feature as having the required characteristics or capabilitiesof the unmodified feature. In general, but subject to the precedingdiscussion, a numerical value herein that is modified by a word ofapproximation such as “approximately” may vary from the stated value by±0.5%, ±1%, ±2%, ±3%, ±4%, ±5%, ±10%, ±12%, or ±15%.

As used herein, the terms “first,” “second,” “third,” etc. may be usedas labels for nouns that they precede, and these terms may notnecessarily imply a particular ordering (e.g., a particular spatial,temporal, or logical ordering). As an example, a system may be describedas determining a “first result” and a “second result,” and the terms“first” and “second” may not necessarily imply that the first result isdetermined before the second result.

As used herein, the terms “based on” and “based at least in part on” maybe used to describe or present one or more factors that affect adetermination, and these terms may not exclude additional factors thatmay affect a determination. A determination may be based solely on thosefactors which are presented or may be based at least in part on thosefactors. The phrase “determine A based on B” indicates that B is afactor that affects the determination of A. In some instances, otherfactors may also contribute to the determination of A. In otherinstances, A may be determined based solely on B.

What is claimed is:
 1. A lidar system comprising: a solid-state laserconfigured to emit pulses of light, wherein the solid-state lasercomprises a passively Q-switched laser comprising a gain medium and asaturable absorber, wherein the saturable absorber is bonded to the gainmedium; a scanner configured to scan the emitted pulses of light acrossa field of regard; a receiver configured to detect at least a portion ofthe scanned pulses of light scattered by a target located a distancefrom the lidar system; and a processor configured to determine thedistance from the lidar system to the target based at least in part on around-trip time of flight for an emitted pulse of light to travel fromthe lidar system to the target and back to the lidar system.
 2. Thelidar system of claim 1, wherein the pulses of light are emitted by theQ-switched laser, and the pulses of light have a pulse repetitionfrequency greater than or equal to 20 kHz.
 3. The lidar system of claim1, wherein the pulses of light are emitted by the Q-switched laser, andthe pulses of light have optical characteristics comprising: a pulseduration less than or equal to 20 nanoseconds; a duty cycle less than orequal to 1%; a pulse energy greater than or equal to 10 nanojoules; anda peak power greater than or equal to 1 watt.
 4. The lidar system ofclaim 1, wherein the saturable absorber comprises vanadium-doped yttriumaluminum garnet (V:YAG), chromium-doped YAG (Cr:YAG), cobalt-dopedMgAl₂O₄ (Co:spinel), neodymium-doped strontium fluoride (Nd:SrF₂), orlithium fluoride with F₂ ⁻ color centers (LiF:F₂ ⁻).
 5. The lidar systemof claim 1, wherein the gain medium comprises neodymium-doped yttriumaluminum garnet (Nd:YAG), ytterbium-doped yttrium aluminum garnet(Yb:YAG), neodymium-doped yttrium orthovanadate (Nd:YVO₄),neodymium-doped yttrium scandium gallium garnet (Nd:YSGG),neodymium-doped gadolinium scandium gallium garnet (Nd:GSGG),neodymium-doped yttrium aluminum perovskite (Nd:YAP), or neodymium-dopedyttrium lithium fluoride (Nd:YLF).
 6. The lidar system of claim 1,wherein the gain medium comprises a back surface with a dielectriccoating having a low reflectivity at a pump-laser wavelength and a highreflectivity at an operating wavelength of the Q-switched laser.
 7. Thelidar system of claim 1, wherein the gain medium is pumped at a pumpwavelength between approximately 800 nm and approximately 1000 nm by anedge-emitter laser diode or a vertical-external-cavity surface-emittinglaser.
 8. The lidar system of claim 1, wherein the Q-switched laser isan eye-safe laser with an operating wavelength between approximately1400 nm and approximately 1600 nm.
 9. The lidar system of claim 1,wherein an operating wavelength of the Q-switched laser is approximately1030 nanometers, approximately 1064 nanometers, or between approximately1400 nanometers and approximately 1480 nanometers.
 10. The lidar systemof claim 1, wherein the Q-switched laser further comprises an end capcoupled to the gain medium, wherein: the end cap is substantially freeof gain-material dopants; and the end cap is positioned to receive lightfrom a pump laser so that the pump-laser light propagates through theend cap before entering the gain medium.
 11. The lidar system of claim1, further comprising a splitter configured to receive the pulses oflight emitted by the solid-state laser and split each received pulse oflight into two or more angularly separated pulses of light which arescanned by the scanner across the field of regard.
 12. The lidar systemof claim 11, wherein: the angularly separated pulses of light arescanned along a scanning direction; and the angularly separated pulsesof light are split along a direction that is approximately orthogonal tothe scanning direction.
 13. The lidar system of claim 11, wherein thereceiver comprises an array of two or more detector elements, whereineach detector element is configured to detect scattered light from arespective pulse of the two or more angularly separated pulses of lightwhich are scanned across the field of regard.
 14. The lidar system ofclaim 1, wherein the field of regard comprises: a horizontal field ofregard greater than or equal to 25 degrees; and a vertical field ofregard greater than or equal to 5 degrees.
 15. The lidar system of claim1, wherein the scanner comprises one or more mirrors, wherein eachmirror is mechanically driven by a galvanometer scanner, a resonantscanner, a microelectromechanical systems (MEMS) device, or a voice coilmotor.
 16. The lidar system of claim 1, wherein: an output beam of thelidar system comprises the emitted pulses of light which are scannedacross the field of regard; an input beam of the lidar system comprisesthe portion of the scanned pulses of light detected by the receiver; andthe input and output beams are substantially coaxial.
 17. The lidarsystem of claim 1, wherein: scanning the emitted pulses of light acrossthe field of regard comprises scanning a field of view of thesolid-state laser across the field of regard; and the scanner is furtherconfigured to scan a field of view of the receiver across the field ofregard, wherein the solid-state laser field of view and the receiverfield of view are scanned synchronously with respect to one another. 18.A lidar system comprising: a solid-state laser configured to emit pulsesof light, wherein the solid-state laser comprises: a Q-switched lasercomprising a gain medium and a Q-switch, wherein the Q-switched laser isconfigured to produce pump pulses of light at a pump wavelength; and anoptical parametric oscillator (OPO) comprising an OPO medium configuredto: receive the pump pulses from the pump laser; convert at least partof the received pump pulses into pulses of light at a signal wavelengthand pulses of light at an idler wavelength; and emit at least a portionof the signal pulses, wherein the pulses of light emitted by thesolid-state laser comprise the signal pulses emitted by the OPO; ascanner configured to scan the emitted pulses of light across a field ofregard; a receiver configured to detect at least a portion of thescanned pulses of light scattered by a target located a distance fromthe lidar system; and a processor configured to determine the distancefrom the lidar system to the target based at least in part on around-trip time of flight for an emitted pulse of light to travel fromthe lidar system to the target and back to the lidar system.
 19. Thelidar system of claim 18, wherein the signal pulses of light emitted bythe OPO have a pulse repetition frequency greater than or equal to 20kHz.
 20. The lidar system of claim 18, wherein the signal pulses oflight emitted by the OPO have optical characteristics comprising: apulse duration less than or equal to 20 nanoseconds; a duty cycle lessthan or equal to 1%; a pulse energy greater than or equal to 10nanojoules; and a peak power greater than or equal to 1 watt.
 21. Thelidar system of claim 18, wherein the pump wavelength is approximately1030 nm or approximately 1064 nm.
 22. The lidar system of claim 18,wherein the pump wavelength (λ_(p)), signal wavelength (λ_(s)), andidler wavelength (λ_(i)) are at least approximately related by anexpression 1/λ_(p)=1/λ_(s)+1/λ_(i), wherein: λ_(p) is less than λ_(s)and λ_(i); and λ_(s) is less than λ_(i).
 23. The lidar system of claim18, wherein the OPO is an eye-safe light source and the signalwavelength of the signal pulses emitted by the OPO is betweenapproximately 1400 nm and approximately 1600 nm.
 24. The lidar system ofclaim 18, wherein the OPO medium comprises periodically poled potassiumtitanyl phosphate (PPKTP), periodically poled potassium titanyl arsenate(PPKTA), periodically poled rubidium titanyl arsenate (PPRTA),periodically poled lithium niobate (PPLN), periodically poled lithiumtantalate (PPLT), or periodically poled stoichiometric lithium tantalate(PPSLT).
 25. The lidar system of claim 18, wherein the OPO mediumcomprises a back surface and an output surface, wherein: the backsurface comprises a dielectric coating with low reflectivity for thepump wavelength and high reflectivity for the signal wavelength; and theoutput surface comprises a dielectric coating with high reflectivity forthe pump wavelength and low or partial reflectivity for the signalwavelength.
 26. The lidar system of claim 25, wherein: the coating ofthe back surface additionally has high reflectivity or low reflectivityfor the idler wavelength; and the coating of the output surfaceadditionally has high reflectivity or low reflectivity for the idlerwavelength.
 27. A lidar system comprising: a solid-state laserconfigured to emit pulses of light, wherein the solid-state lasercomprises a Q-switched laser comprising a gain medium and a Q-switch,wherein the pulses of light are emitted by the Q-switched laser, and thepulses of light have optical characteristics comprising: a pulseduration less than or equal to 20 nanoseconds; a duty cycle less than orequal to 1%; a pulse energy greater than or equal to 10 nanojoules; anda peak power greater than or equal to 1 watt; a scanner configured toscan the emitted pulses of light across a field of regard; a receiverconfigured to detect at least a portion of the scanned pulses of lightscattered by a target located a distance from the lidar system; and aprocessor configured to determine the distance from the lidar system tothe target based at least in part on a round-trip time of flight for anemitted pulse of light to travel from the lidar system to the target andback to the lidar system.
 28. The lidar system of claim 27, wherein thepulses of light have a pulse repetition frequency greater than or equalto 20 kHz.
 29. The lidar system of claim 27, wherein the Q-switchedlaser is an actively Q-switched laser and the Q-switch is an activeQ-switch.
 30. The lidar system of claim 27, wherein the Q-switched laseris a passively Q-switched (PQSW) laser and the Q-switch is a saturableabsorber.